diff --git a/Swashbuckle.OData.Sample/ODataControllers/OrdersController.cs b/Swashbuckle.OData.Sample/ODataControllers/OrdersController.cs
index e89f3e4..c79e48b 100644
--- a/Swashbuckle.OData.Sample/ODataControllers/OrdersController.cs
+++ b/Swashbuckle.OData.Sample/ODataControllers/OrdersController.cs
@@ -26,7 +26,7 @@ public IQueryable<Order> GetOrders()
         }
 
         /// <summary>
-        /// Create a new order for the customer with the given <paramref name="customerId"/>
+        /// Create a new order for the customer with the given id
         /// </summary>
         /// <param name="customerId">The customer id</param>
         /// <param name="order">Order details</param>
@@ -34,6 +34,7 @@ public IQueryable<Order> GetOrders()
         public async Task<IHttpActionResult> Post([FromODataUri] int customerId, Order order)
         {
             order.OrderId = SequentialGuidGenerator.Generate(SequentialGuidType.SequentialAtEnd);
+            order.CustomerId = customerId;
 
             if (!ModelState.IsValid)
             {
diff --git a/Swashbuckle.OData/Descriptions/EdmLibHelpers.cs b/Swashbuckle.OData/Descriptions/EdmLibHelpers.cs
index 3e030ab..ca5c7ad 100644
--- a/Swashbuckle.OData/Descriptions/EdmLibHelpers.cs
+++ b/Swashbuckle.OData/Descriptions/EdmLibHelpers.cs
@@ -103,8 +103,8 @@ public static IEdmType GetEdmType(this IEdmModel edmModel, Type clrType)
 
         private static IEdmType GetEdmType(IEdmModel edmModel, Type clrType, bool testCollections)
         {
-            Contract.Assert(edmModel != null);
-            Contract.Assert(clrType != null);
+            Contract.Requires(edmModel != null);
+            Contract.Requires(clrType != null);
 
             var primitiveType = GetEdmPrimitiveTypeOrNull(clrType);
             if (primitiveType != null)
@@ -160,6 +160,8 @@ private static IEdmType GetEdmType(IEdmModel edmModel, Type clrType, bool testCo
 
         public static IEdmTypeReference GetEdmTypeReference(this IEdmModel edmModel, Type clrType)
         {
+            Contract.Requires(clrType != null);
+
             var edmType = edmModel.GetEdmType(clrType);
             if (edmType != null)
             {
@@ -172,7 +174,7 @@ public static IEdmTypeReference GetEdmTypeReference(this IEdmModel edmModel, Typ
 
         public static IEdmTypeReference ToEdmTypeReference(this IEdmType edmType, bool isNullable)
         {
-            Contract.Assert(edmType != null);
+            Contract.Requires(edmType != null);
 
             switch (edmType.TypeKind)
             {
@@ -229,9 +231,9 @@ public static Type GetClrType(IEdmType edmType, IEdmModel edmModel)
 
         public static Type GetClrType(IEdmType edmType, IEdmModel edmModel, IAssembliesResolver assembliesResolver)
         {
-            var edmSchemaType = edmType as IEdmSchemaType;
+            Contract.Requires(edmType is IEdmSchemaType);
 
-            Contract.Assert(edmSchemaType != null);
+            var edmSchemaType = (IEdmSchemaType) edmType;
 
             var annotation = edmModel.GetAnnotationValue<ClrTypeAnnotation>(edmSchemaType);
             if (annotation != null)
@@ -291,8 +293,8 @@ public static bool IsAutoExpand(IEdmProperty edmProperty, IEdmModel edmModel)
 
         private static QueryableRestrictionsAnnotation GetPropertyRestrictions(IEdmProperty edmProperty, IEdmModel edmModel)
         {
-            Contract.Assert(edmProperty != null);
-            Contract.Assert(edmModel != null);
+            Contract.Requires(edmProperty != null);
+            Contract.Requires(edmModel != null);
 
             return edmModel.GetAnnotationValue<QueryableRestrictionsAnnotation>(edmProperty);
         }
@@ -332,12 +334,16 @@ public static PropertyInfo GetDynamicPropertyDictionary(IEdmStructuredType edmTy
 
         public static IEdmPrimitiveType GetEdmPrimitiveTypeOrNull(Type clrType)
         {
+            Contract.Requires(clrType != null);
+
             IEdmPrimitiveType primitiveType;
             return BuiltInTypesMapping.TryGetValue(clrType, out primitiveType) ? primitiveType : null;
         }
 
         public static IEdmPrimitiveTypeReference GetEdmPrimitiveTypeReferenceOrNull(Type clrType)
         {
+            Contract.Requires(clrType != null);
+
             var primitiveType = GetEdmPrimitiveTypeOrNull(clrType);
             return primitiveType != null ? CoreModel.GetPrimitive(primitiveType.PrimitiveKind, IsNullable(clrType)) : null;
         }
@@ -346,6 +352,8 @@ public static IEdmPrimitiveTypeReference GetEdmPrimitiveTypeReferenceOrNull(Type
         // and returns the corresponding clr type to which we map like uint => long.
         public static Type IsNonstandardEdmPrimitive(Type type, out bool isNonstandardEdmPrimitive)
         {
+            Contract.Requires(type != null);
+
             var edmType = GetEdmPrimitiveTypeReferenceOrNull(type);
             if (edmType == null)
             {
@@ -363,19 +371,23 @@ public static Type IsNonstandardEdmPrimitive(Type type, out bool isNonstandardEd
         // to a valid EDM literal (the C# type name IEnumerable<int>).
         public static string EdmName(this Type clrType)
         {
+            Contract.Requires(clrType != null);
+
             // We cannot use just Type.Name here as it doesn't work for generic types.
             return MangleClrTypeName(clrType);
         }
 
         public static string EdmFullName(this Type clrType)
         {
+            Contract.Requires(clrType != null);
+
             return string.Format(CultureInfo.InvariantCulture, "{0}.{1}", clrType.Namespace, clrType.EdmName());
         }
 
         public static IEnumerable<IEdmStructuralProperty> GetConcurrencyProperties(this IEdmModel model, IEdmEntitySet entitySet)
         {
-            Contract.Assert(model != null);
-            Contract.Assert(entitySet != null);
+            Contract.Requires(model != null);
+            Contract.Requires(entitySet != null);
 
             IEnumerable<IEdmStructuralProperty> cachedProperties;
             if (_concurrencyProperties != null && _concurrencyProperties.TryGetValue(entitySet, out cachedProperties))
@@ -427,6 +439,8 @@ private static IEdmPrimitiveType GetPrimitiveType(EdmPrimitiveTypeKind primitive
 
         public static bool IsNullable(Type type)
         {
+            Contract.Requires(type != null);
+
             return !type.IsValueType || Nullable.GetUnderlyingType(type) != null;
         }
 
@@ -438,13 +452,15 @@ private static Type ExtractGenericInterface(Type queryType, Type interfaceType)
 
         private static IEnumerable<Type> GetMatchingTypes(string edmFullName, IAssembliesResolver assembliesResolver)
         {
+            Contract.Requires(assembliesResolver != null);
+
             return TypeHelper.GetLoadedTypes(assembliesResolver).Where(t => t.IsPublic && t.EdmFullName() == edmFullName);
         }
 
         // TODO (workitem 336): Support nested types and anonymous types.
         private static string MangleClrTypeName(Type type)
         {
-            Contract.Assert(type != null);
+            Contract.Requires(type != null);
 
             return !type.IsGenericType 
                 ? type.Name 
diff --git a/Swashbuckle.OData/Descriptions/HttpActionDescriptorExtensions.cs b/Swashbuckle.OData/Descriptions/HttpActionDescriptorExtensions.cs
index cc8ab78..6d0e42c 100644
--- a/Swashbuckle.OData/Descriptions/HttpActionDescriptorExtensions.cs
+++ b/Swashbuckle.OData/Descriptions/HttpActionDescriptorExtensions.cs
@@ -1,4 +1,5 @@
-using System.Linq;
+using System.Diagnostics.Contracts;
+using System.Linq;
 using System.Web.Http;
 using System.Web.Http.Controllers;
 using System.Web.Http.Description;
@@ -9,6 +10,8 @@ internal static class HttpActionDescriptorExtensions
     {
         public static ResponseDescription CreateResponseDescription(this HttpActionDescriptor actionDescriptor)
         {
+            Contract.Requires(actionDescriptor != null);
+
             var responseTypeAttribute = actionDescriptor.GetCustomAttributes<ResponseTypeAttribute>();
             var responseType = responseTypeAttribute.Select(attribute => attribute.ResponseType).FirstOrDefault();
 
@@ -22,6 +25,8 @@ public static ResponseDescription CreateResponseDescription(this HttpActionDescr
 
         private static string GetApiResponseDocumentation(this HttpActionDescriptor actionDescriptor)
         {
+            Contract.Requires(actionDescriptor != null);
+
             var documentationProvider = actionDescriptor.Configuration.Services.GetDocumentationProvider();
             return documentationProvider?.GetResponseDocumentation(actionDescriptor);
         }
diff --git a/Swashbuckle.OData/Descriptions/IODataRouteGenerator.cs b/Swashbuckle.OData/Descriptions/IODataRouteGenerator.cs
index 89e4f01..f9483af 100644
--- a/Swashbuckle.OData/Descriptions/IODataRouteGenerator.cs
+++ b/Swashbuckle.OData/Descriptions/IODataRouteGenerator.cs
@@ -16,7 +16,7 @@ public interface IODataRouteGenerator
     }
 
     [ContractClassFor(typeof(IODataRouteGenerator))]
-    public sealed class ODataRouteGeneratorContract : IODataRouteGenerator
+    public abstract class ODataRouteGeneratorContract : IODataRouteGenerator
     {
         public List<SwaggerRoute> Generate(string routePrefix, IEdmModel model)
         {
diff --git a/Swashbuckle.OData/Descriptions/IParameterMapper.cs b/Swashbuckle.OData/Descriptions/IParameterMapper.cs
index 6acdd06..1656820 100644
--- a/Swashbuckle.OData/Descriptions/IParameterMapper.cs
+++ b/Swashbuckle.OData/Descriptions/IParameterMapper.cs
@@ -18,7 +18,7 @@ public interface IParameterMapper
     }
 
     [ContractClassFor(typeof(IParameterMapper))]
-    public sealed class ParameterMapperContract : IParameterMapper
+    public abstract class ParameterMapperContract : IParameterMapper
     {
         public HttpParameterDescriptor Map(Parameter swaggerParameter, int parameterIndex, HttpActionDescriptor actionDescriptor)
         {
diff --git a/Swashbuckle.OData/Descriptions/ODataApiExplorer.cs b/Swashbuckle.OData/Descriptions/ODataApiExplorer.cs
index 6c3e321..92a0ed5 100644
--- a/Swashbuckle.OData/Descriptions/ODataApiExplorer.cs
+++ b/Swashbuckle.OData/Descriptions/ODataApiExplorer.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.Diagnostics.Contracts;
 using System.Linq;
 using System.Net.Http;
 using System.Net.Http.Formatting;
@@ -63,6 +64,8 @@ private Collection<ApiDescription> GetApiDescriptions()
         /// <returns></returns>
         private List<ApiDescription> GetApiDescriptions(ODataRoute oDataRoute)
         {
+            Contract.Requires(oDataRoute != null);
+
             var apiDescriptions = new List<ApiDescription>();
 
             var standardRoutes = _routeGenerator.Generate(oDataRoute.RoutePrefix, oDataRoute.GetEdmModel());
@@ -79,6 +82,8 @@ private List<ApiDescription> GetApiDescriptions(ODataRoute oDataRoute)
 
         private List<ApiDescription> GetApiDescriptions(ODataRoute oDataRoute, SwaggerRoute potentialSwaggerRoute)
         {
+            Contract.Requires(potentialSwaggerRoute != null);
+
             var apiDescriptions = new List<ApiDescription>();
 
             apiDescriptions.AddIfNotNull(GetApiDescription(new HttpMethod("DELETE"), potentialSwaggerRoute.PathItem.delete, potentialSwaggerRoute.Template, oDataRoute));
@@ -134,6 +139,8 @@ private HttpRequestMessage CreateHttpRequestMessage(HttpMethod httpMethod, Opera
 
         private ApiDescription GetApiDescription(HttpActionDescriptor actionDescriptor, HttpMethod httpMethod, Operation operation, string potentialPathTemplate, ODataRoute oDataRoute)
         {
+            Contract.Requires(actionDescriptor == null || operation != null);
+
             if (actionDescriptor == null)
             {
                 return null;
@@ -212,11 +219,15 @@ private static HttpActionDescriptor MapForRestierIfNecessary(HttpActionDescripto
 
         private static IEnumerable<MediaTypeFormatter> GetInnerFormatters(IEnumerable<MediaTypeFormatter> mediaTypeFormatters)
         {
+            Contract.Requires(mediaTypeFormatters != null);
+
             return mediaTypeFormatters.Select(Decorator.GetInner);
         }
 
         private List<SwaggerApiParameterDescription> CreateParameterDescriptions(Operation operation, HttpActionDescriptor actionDescriptor)
         {
+            Contract.Requires(operation != null);
+
             return operation.parameters.Select((parameter, index) => GetParameterDescription(parameter, index, actionDescriptor)).ToList();
         }
 
@@ -242,6 +253,8 @@ private HttpParameterDescriptor GetHttpParameterDescriptor(Parameter parameter,
 
         private static string GetApiParameterDocumentation(Parameter parameter, HttpParameterDescriptor parameterDescriptor)
         {
+            Contract.Requires(parameterDescriptor != null);
+
             var documentationProvider = parameterDescriptor.Configuration.Services.GetDocumentationProvider();
 
             return documentationProvider != null 
@@ -251,6 +264,8 @@ private static string GetApiParameterDocumentation(Parameter parameter, HttpPara
 
         private static string GetApiDocumentation(HttpActionDescriptor actionDescriptor, Operation operation)
         {
+            Contract.Requires(actionDescriptor != null);
+
             var documentationProvider = actionDescriptor.Configuration.Services.GetDocumentationProvider();
             return documentationProvider != null 
                 ? documentationProvider.GetDocumentation(actionDescriptor) 
@@ -284,5 +299,11 @@ private static IEnumerable<IHttpRoute> FlattenRoutes(IEnumerable<IHttpRoute> rou
                 }
             }
         }
+
+        [ContractInvariantMethod]
+        private void ObjectInvariant()
+        {
+            Contract.Invariant(_apiDescriptions != null);
+        }
     }
 }
\ No newline at end of file
diff --git a/Swashbuckle.OData/Descriptions/ODataRouteExtensions.cs b/Swashbuckle.OData/Descriptions/ODataRouteExtensions.cs
index f58763f..243d94f 100644
--- a/Swashbuckle.OData/Descriptions/ODataRouteExtensions.cs
+++ b/Swashbuckle.OData/Descriptions/ODataRouteExtensions.cs
@@ -1,4 +1,5 @@
-using System.Linq;
+using System.Diagnostics.Contracts;
+using System.Linq;
 using System.Web.OData.Routing;
 using Microsoft.OData.Edm;
 
@@ -8,11 +9,15 @@ public static class ODataRouteExtensions
     {
         public static IEdmModel GetEdmModel(this ODataRoute oDataRoute)
         {
+            Contract.Requires(oDataRoute != null);
+
             return oDataRoute.GetODataPathRouteConstraint().EdmModel;
         }
 
         public static ODataPathRouteConstraint GetODataPathRouteConstraint(this ODataRoute oDataRoute)
         {
+            Contract.Requires(oDataRoute != null);
+
             return oDataRoute.Constraints.Values.SingleOrDefault(value => value is ODataPathRouteConstraint) as ODataPathRouteConstraint;
         }
     }
diff --git a/Swashbuckle.OData/Descriptions/ODataSwaggerUtilities.cs b/Swashbuckle.OData/Descriptions/ODataSwaggerUtilities.cs
index b8600a0..c5c4e47 100644
--- a/Swashbuckle.OData/Descriptions/ODataSwaggerUtilities.cs
+++ b/Swashbuckle.OData/Descriptions/ODataSwaggerUtilities.cs
@@ -294,6 +294,8 @@ public static PathItem CreateSwaggerPathForOperationOfEntity(IEdmOperation opera
         /// <returns></returns>
         public static Url GetPathForEntitySet(string routePrefix, IEdmEntitySet entitySet)
         {
+            Contract.Requires(entitySet != null);
+
             return routePrefix.AppendPathSegment(entitySet.Name);
         }
 
@@ -617,12 +619,17 @@ private static string GetPrimitiveTypeAndFormat(IEdmPrimitiveType primitiveType,
 
         private static Operation Responses(this Operation obj, IDictionary<string, Response> responses)
         {
+            Contract.Requires(obj != null);
+
             obj.responses = responses;
             return obj;
         }
 
         private static IDictionary<string, Response> ResponseRef(this IDictionary<string, Response> responses, string name, string description, string refType)
         {
+            Contract.Requires(responses != null);
+            Contract.Requires(name != null);
+
             responses.Add(name, new Response
             {
                 description = description,
@@ -637,6 +644,9 @@ private static IDictionary<string, Response> ResponseRef(this IDictionary<string
 
         private static IDictionary<string, Response> Response(this IDictionary<string, Response> responses, string name, string description, IEdmType type)
         {
+            Contract.Requires(responses != null);
+            Contract.Requires(name != null);
+
             var schema = new Schema();
             SetSwaggerType(schema, type);
 
@@ -651,11 +661,16 @@ private static IDictionary<string, Response> Response(this IDictionary<string, R
 
         private static IDictionary<string, Response> DefaultErrorResponse(this IDictionary<string, Response> responses)
         {
+            Contract.Requires(responses != null);
+
             return responses.ResponseRef("default", "Unexpected error", "#/definitions/_Error");
         }
 
         private static IDictionary<string, Response> Response(this IDictionary<string, Response> responses, string name, string description)
         {
+            Contract.Requires(responses != null);
+            Contract.Requires(name != null);
+
             responses.Add(name, new Response
             {
                 description = description
@@ -666,12 +681,16 @@ private static IDictionary<string, Response> Response(this IDictionary<string, R
 
         private static Operation Parameters(this Operation obj, IList<Parameter> parameters)
         {
+            Contract.Requires(obj != null);
+
             obj.parameters = parameters;
             return obj;
         }
 
         private static IList<Parameter> Parameter(this IList<Parameter> parameters, string name, string kind, string description, string type, bool required, string format = null)
         {
+            Contract.Requires(parameters != null);
+
             parameters.Add(new Parameter
             {
                 name = name,
@@ -687,6 +706,9 @@ private static IList<Parameter> Parameter(this IList<Parameter> parameters, stri
 
         internal static IList<Parameter> Parameter(this IList<Parameter> parameters, string name, string kind, string description, IEdmType type)
         {
+            Contract.Requires(parameters != null);
+            Contract.Requires(type != null);
+
             var parameter = new Parameter
             {
                 name = name,
@@ -711,30 +733,40 @@ internal static IList<Parameter> Parameter(this IList<Parameter> parameters, str
 
         private static Operation Tags(this Operation obj, params string[] tags)
         {
+            Contract.Requires(obj != null);
+
             obj.tags = tags;
             return obj;
         }
 
         private static Operation Summary(this Operation obj, string summary)
         {
+            Contract.Requires(obj != null);
+
             obj.summary = summary;
             return obj;
         }
 
         private static Operation Description(this Operation obj, string description)
         {
+            Contract.Requires(obj != null);
+
             obj.description = description;
             return obj;
         }
 
         private static Schema Description(this Schema obj, string description)
         {
+            Contract.Requires(obj != null);
+
             obj.description = description;
             return obj;
         }
 
         private static Operation OperationId(this Operation obj, string operationId)
         {
+            Contract.Requires(obj != null);
+
             obj.operationId = operationId;
             return obj;
         }
diff --git a/Swashbuckle.OData/Descriptions/OperationBuilder.cs b/Swashbuckle.OData/Descriptions/OperationBuilder.cs
index 21dcdfc..49fbee5 100644
--- a/Swashbuckle.OData/Descriptions/OperationBuilder.cs
+++ b/Swashbuckle.OData/Descriptions/OperationBuilder.cs
@@ -25,6 +25,7 @@ public OperationBuilder(Operation operation, SwaggerRouteBuilder swaggerRouteBui
         public OperationBuilder PathParameter<T>(string parameterName)
         {
             Contract.Requires(!string.IsNullOrWhiteSpace(parameterName));
+            Contract.Ensures(Contract.Result<OperationBuilder>() != null);
 
             _operation.Parameters().Parameter(parameterName, ParameterSource.Path.ToString().ToLower(), null, GetEdmModel().GetEdmType(typeof (T)));
 
@@ -39,6 +40,7 @@ public OperationBuilder PathParameter<T>(string parameterName)
         public OperationBuilder BodyParameter<T>(string parameterName)
         {
             Contract.Requires(!string.IsNullOrWhiteSpace(parameterName));
+            Contract.Ensures(Contract.Result<OperationBuilder>() != null);
 
             _operation.Parameters().Parameter(parameterName, ParameterSource.Body.ToString().ToLower(), null, GetEdmModel().GetEdmType(typeof (T)));
 
@@ -49,5 +51,11 @@ private IEdmModel GetEdmModel()
         {
             return _swaggerRouteBuilder.ODataRoute.GetEdmModel();
         }
+
+        [ContractInvariantMethod]
+        private void ObjectInvariant()
+        {
+            Contract.Invariant(_swaggerRouteBuilder != null);
+        }
     }
 }
\ No newline at end of file
diff --git a/Swashbuckle.OData/Descriptions/OperationExtensions.cs b/Swashbuckle.OData/Descriptions/OperationExtensions.cs
index ae116c1..39f61f2 100644
--- a/Swashbuckle.OData/Descriptions/OperationExtensions.cs
+++ b/Swashbuckle.OData/Descriptions/OperationExtensions.cs
@@ -19,6 +19,7 @@ public static IDictionary<string, string> GenerateSampleQueryParameterValues(thi
         public static string GenerateSampleODataAbsoluteUri(this Operation operation, string serviceRoot, string pathTemplate)
         {
             Contract.Requires(operation != null);
+            Contract.Requires(serviceRoot != null);
 
             var uriTemplate = new UriTemplate(pathTemplate);
 
diff --git a/Swashbuckle.OData/Descriptions/ParameterExtensions.cs b/Swashbuckle.OData/Descriptions/ParameterExtensions.cs
index 53e8e55..3480092 100644
--- a/Swashbuckle.OData/Descriptions/ParameterExtensions.cs
+++ b/Swashbuckle.OData/Descriptions/ParameterExtensions.cs
@@ -9,6 +9,8 @@ internal static class ParameterExtensions
     {
         public static ParameterSource MapSource(this Parameter parameter)
         {
+            Contract.Requires(parameter != null);
+
             switch (parameter.@in)
             {
                 case "query":
@@ -28,6 +30,8 @@ public static ParameterSource MapSource(this Parameter parameter)
 
         public static Type GetClrType(this Parameter parameter)
         {
+            Contract.Requires(parameter != null);
+
             var type = parameter.type;
             var format = parameter.format;
 
@@ -70,6 +74,7 @@ public static Type GetClrType(this Parameter parameter)
 
         public static string GenerateSamplePathParameterValue(this Parameter parameter)
         {
+            Contract.Requires(parameter != null);
             Contract.Requires(parameter.@in == "path");
 
             var type = parameter.type;
@@ -111,6 +116,7 @@ public static string GenerateSamplePathParameterValue(this Parameter parameter)
 
         private static Type GetEntityTypeForBodyParameter(Parameter parameter)
         {
+            Contract.Requires(parameter != null);
             Contract.Requires(parameter.@in == "body");
 
             var fullTypeName = parameter.schema.@ref.Replace("#/definitions/", string.Empty);
@@ -120,6 +126,7 @@ private static Type GetEntityTypeForBodyParameter(Parameter parameter)
 
         public static Type GetEntityType(this Schema schema)
         {
+            Contract.Requires(schema != null);
             Contract.Requires(!string.IsNullOrWhiteSpace(schema.@ref));
 
             var fullTypeName = schema.@ref.Replace("#/definitions/", string.Empty);
@@ -129,6 +136,7 @@ public static Type GetEntityType(this Schema schema)
 
         public static Type GetEntitySetType(this Schema schema)
         {
+            Contract.Requires(schema != null);
             Contract.Requires(schema.type == "array");
 
             var queryableType = typeof(IQueryable<>);
diff --git a/Swashbuckle.OData/Descriptions/RestierParameterDescriptor.cs b/Swashbuckle.OData/Descriptions/RestierParameterDescriptor.cs
index 5ac2c7b..37a9533 100644
--- a/Swashbuckle.OData/Descriptions/RestierParameterDescriptor.cs
+++ b/Swashbuckle.OData/Descriptions/RestierParameterDescriptor.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Collections.ObjectModel;
+using System.Diagnostics.Contracts;
 using System.Web.Http;
 using System.Web.Http.Controllers;
 using Swashbuckle.Swagger;
@@ -10,6 +11,8 @@ internal class RestierParameterDescriptor : HttpParameterDescriptor
     {
         public RestierParameterDescriptor(Parameter parameter)
         {
+            Contract.Requires(parameter != null);
+
             Parameter = parameter;
             DefaultValue = null;
             Prefix = null;
diff --git a/Swashbuckle.OData/Descriptions/SwaggerPathGenerator.cs b/Swashbuckle.OData/Descriptions/SwaggerPathGenerator.cs
index e7ac3ca..37b9fd2 100644
--- a/Swashbuckle.OData/Descriptions/SwaggerPathGenerator.cs
+++ b/Swashbuckle.OData/Descriptions/SwaggerPathGenerator.cs
@@ -2,6 +2,7 @@
 // Licensed under the MIT License.  See License.txt in the project root for license information.
 
 using System.Collections.Generic;
+using System.Diagnostics.Contracts;
 using System.Linq;
 using Microsoft.OData.Edm;
 
@@ -23,6 +24,8 @@ public List<SwaggerRoute> Generate(string routePrefix, IEdmModel model)
 
         private static IEnumerable<SwaggerRoute> GenerateEntitySetRoutes(string routePrefix, IEdmModel model)
         {
+            Contract.Requires(model != null);
+
             return model.EntityContainer
                 .EntitySets()
                 .Select(entitySet => new SwaggerRoute(ODataSwaggerUtilities.GetPathForEntitySet(routePrefix, entitySet), ODataSwaggerUtilities.CreateSwaggerPathForEntitySet(entitySet)));
@@ -30,6 +33,8 @@ private static IEnumerable<SwaggerRoute> GenerateEntitySetRoutes(string routePre
 
         private static IEnumerable<SwaggerRoute> GenerateEntityRoutes(string routePrefix, IEdmModel model)
         {
+            Contract.Requires(model != null);
+
             return model.EntityContainer
                 .EntitySets()
                 .Select(entitySet => new SwaggerRoute(ODataSwaggerUtilities.GetPathForEntity(routePrefix, entitySet), ODataSwaggerUtilities.CreateSwaggerPathForEntity(entitySet)));
@@ -37,6 +42,8 @@ private static IEnumerable<SwaggerRoute> GenerateEntityRoutes(string routePrefix
 
         private static IEnumerable<SwaggerRoute> GenerateOperationImportRoutes(string routePrefix, IEdmModel model)
         {
+            Contract.Requires(model != null);
+
             return model.EntityContainer
                 .OperationImports()
                 .Select(operationImport => new SwaggerRoute(ODataSwaggerUtilities.GetPathForOperationImport(routePrefix, operationImport), ODataSwaggerUtilities.CreateSwaggerPathForOperationImport(operationImport)));
@@ -50,6 +57,8 @@ private static IEnumerable<SwaggerRoute> GenerateOperationImportRoutes(string ro
         /// <returns></returns>
         private static IEnumerable<SwaggerRoute> GenerateOperationRoutes(string routePrefix, IEdmModel model)
         {
+            Contract.Requires(model != null);
+
             var routes = new List<SwaggerRoute>();
 
             foreach (var operation in model.SchemaElements.OfType<IEdmOperation>())
diff --git a/Swashbuckle.OData/Descriptions/SwaggerRouteBuilder.cs b/Swashbuckle.OData/Descriptions/SwaggerRouteBuilder.cs
index df20ef1..0987c30 100644
--- a/Swashbuckle.OData/Descriptions/SwaggerRouteBuilder.cs
+++ b/Swashbuckle.OData/Descriptions/SwaggerRouteBuilder.cs
@@ -22,6 +22,7 @@ public SwaggerRouteBuilder(SwaggerRoute swaggerRoute, ODataRoute oDataRoute)
         public OperationBuilder Operation(HttpMethod httpMethod)
         {
             Contract.Requires(GetOperation(httpMethod) == null);
+            Contract.Ensures(Contract.Result<OperationBuilder>() != null);
 
             var operation = new Operation();
 
@@ -49,8 +50,11 @@ public OperationBuilder Operation(HttpMethod httpMethod)
             return new OperationBuilder(operation, this);
         }
 
+        [Pure]
         public Operation GetOperation(HttpMethod httpMethod)
         {
+            Contract.Requires(httpMethod != null);
+
             switch (httpMethod.Method.ToUpper())
             {
                 case "GET":
@@ -67,5 +71,11 @@ public Operation GetOperation(HttpMethod httpMethod)
                     throw new ArgumentOutOfRangeException(nameof(httpMethod));
             }
         }
+
+        [ContractInvariantMethod]
+        private void ObjectInvariant()
+        {
+            Contract.Invariant(_swaggerRoute != null);
+        }
     }
 }
\ No newline at end of file
diff --git a/Swashbuckle.OData/Descriptions/TypeExtensions.cs b/Swashbuckle.OData/Descriptions/TypeExtensions.cs
index 12abb18..30ec76b 100644
--- a/Swashbuckle.OData/Descriptions/TypeExtensions.cs
+++ b/Swashbuckle.OData/Descriptions/TypeExtensions.cs
@@ -2,6 +2,7 @@
 // Licensed under the MIT License.  See License.txt in the project root for license information.
 
 using System.ComponentModel;
+using System.Diagnostics.Contracts;
 
 namespace System
 {
@@ -13,6 +14,8 @@ internal static class TypeExtensions
     {
         public static bool IsNullable(this Type type)
         {
+            Contract.Requires(type != null);
+
             if (type.IsValueType)
             {
                 // value types are only nullable if they are Nullable<T>
diff --git a/Swashbuckle.OData/Descriptions/TypeHelper.cs b/Swashbuckle.OData/Descriptions/TypeHelper.cs
index 24c78c1..2078092 100644
--- a/Swashbuckle.OData/Descriptions/TypeHelper.cs
+++ b/Swashbuckle.OData/Descriptions/TypeHelper.cs
@@ -16,6 +16,8 @@ internal static class TypeHelper
     {
         public static Type ToNullable(this Type t)
         {
+            Contract.Requires(t != null);
+
             if (t.IsNullable())
             {
                 return t;
@@ -26,6 +28,8 @@ public static Type ToNullable(this Type t)
         // Gets the collection element type.
         public static Type GetInnerElementType(this Type type)
         {
+            Contract.Requires(type != null);
+
             Type elementType;
             type.IsCollection(out elementType);
             Contract.Assert(elementType != null);
@@ -35,6 +39,8 @@ public static Type GetInnerElementType(this Type type)
 
         public static bool IsCollection(this Type type)
         {
+            Contract.Requires(type != null);
+
             Type elementType;
             return type.IsCollection(out elementType);
         }
@@ -42,6 +48,7 @@ public static bool IsCollection(this Type type)
         public static bool IsCollection(this Type type, out Type elementType)
         {
             Contract.Requires(type != null);
+            Contract.Ensures(Contract.ValueAtReturn(out elementType) != null);
 
             elementType = type;
 
@@ -67,11 +74,15 @@ public static bool IsCollection(this Type type, out Type elementType)
 
         public static Type GetUnderlyingTypeOrSelf(Type type)
         {
+            Contract.Requires(type != null);
+
             return Nullable.GetUnderlyingType(type) ?? type;
         }
 
         public static bool IsEnum(Type type)
         {
+            Contract.Requires(type != null);
+
             var underlyingTypeOrSelf = GetUnderlyingTypeOrSelf(type);
             return underlyingTypeOrSelf.IsEnum;
         }
@@ -85,7 +96,7 @@ public static bool IsEnum(Type type)
         /// <returns><c>true</c> if the type is a primitive type.</returns>
         internal static bool IsQueryPrimitiveType(Type type)
         {
-            Contract.Assert(type != null);
+            Contract.Requires(type != null);
 
             type = GetInnerMostElementType(type);
 
@@ -100,7 +111,7 @@ internal static bool IsQueryPrimitiveType(Type type)
         /// <returns>The innermost element type</returns>
         internal static Type GetInnerMostElementType(Type type)
         {
-            Contract.Assert(type != null);
+            Contract.Requires(type != null);
 
             while (true)
             {
@@ -127,6 +138,8 @@ internal static Type GetInnerMostElementType(Type type)
         /// <returns></returns>
         internal static Type GetImplementedIEnumerableType(Type type)
         {
+            Contract.Requires(type != null);
+
             // get inner type from Task<T>
             if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof (Task<>))
             {
@@ -149,6 +162,8 @@ internal static Type GetImplementedIEnumerableType(Type type)
         // This code is copied from DefaultHttpControllerTypeResolver.GetControllerTypes.
         internal static IEnumerable<Type> GetLoadedTypes(IAssembliesResolver assembliesResolver)
         {
+            Contract.Requires(assembliesResolver != null);
+
             var result = new List<Type>();
 
             // Go through all assemblies referenced by the application and search for types matching a predicate
@@ -186,6 +201,8 @@ internal static IEnumerable<Type> GetLoadedTypes(IAssembliesResolver assembliesR
 
         private static Type GetInnerGenericType(Type interfaceType)
         {
+            Contract.Requires(interfaceType != null);
+
             // Getting the type T definition if the returning type implements IEnumerable<T>
             var parameterTypes = interfaceType.GetGenericArguments();
 
diff --git a/Swashbuckle.OData/EqualityComparer.cs b/Swashbuckle.OData/EqualityComparer.cs
index 0bd9909..0b76269 100644
--- a/Swashbuckle.OData/EqualityComparer.cs
+++ b/Swashbuckle.OData/EqualityComparer.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.Contracts;
 
 namespace Swashbuckle.OData
 {
@@ -147,5 +148,12 @@ public int GetHashCode(TSource obj)
             }
             return _comparer.GetHashCode(_projection(obj));
         }
+
+        [ContractInvariantMethod]
+        private void ObjectInvariant()
+        {
+            Contract.Invariant(_projection != null);
+            Contract.Invariant(_comparer != null);
+        }
     }
 }
\ No newline at end of file
diff --git a/Swashbuckle.OData/HttpConfigurationExtensions.cs b/Swashbuckle.OData/HttpConfigurationExtensions.cs
index ccb1ed0..f43befb 100644
--- a/Swashbuckle.OData/HttpConfigurationExtensions.cs
+++ b/Swashbuckle.OData/HttpConfigurationExtensions.cs
@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Diagnostics.Contracts;
 using System.Web;
 using System.Web.Http;
 using System.Web.OData.Routing;
@@ -12,6 +13,8 @@ public static class HttpConfigurationExtensions
     {
         internal static JsonSerializerSettings SerializerSettingsOrDefault(this HttpConfiguration httpConfig)
         {
+            Contract.Requires(httpConfig != null);
+
             var formatter = httpConfig.Formatters.JsonFormatter;
             return formatter != null 
                 ? formatter.SerializerSettings 
@@ -20,6 +23,10 @@ internal static JsonSerializerSettings SerializerSettingsOrDefault(this HttpConf
 
         public static SwaggerRouteBuilder AddCustomSwaggerRoute(this HttpConfiguration httpConfig, ODataRoute oDataRoute, string routeTemplate)
         {
+            Contract.Requires(httpConfig != null);
+            Contract.Requires(oDataRoute != null);
+            Contract.Ensures(Contract.Result<SwaggerRouteBuilder>() != null);
+
             var fullRouteTemplate = HttpUtility.UrlDecode(oDataRoute.RoutePrefix.AppendPathSegment(routeTemplate));
 
             var swaggerRoute = new SwaggerRoute(fullRouteTemplate);
@@ -40,6 +47,10 @@ public static SwaggerRouteBuilder AddCustomSwaggerRoute(this HttpConfiguration h
 
         public static List<SwaggerRoute> GetCustomSwaggerRoutes(this HttpConfiguration httpConfig, ODataRoute oDataRoute)
         {
+            Contract.Requires(httpConfig != null);
+            Contract.Requires(oDataRoute != null);
+            Contract.Ensures(Contract.Result<List<SwaggerRoute>>() != null);
+
             object swaggerRoutes;
             httpConfig.Properties.TryGetValue(oDataRoute, out swaggerRoutes);
 
diff --git a/Swashbuckle.OData/ODataSwaggerProvider.cs b/Swashbuckle.OData/ODataSwaggerProvider.cs
index 3320a98..a6cc12d 100644
--- a/Swashbuckle.OData/ODataSwaggerProvider.cs
+++ b/Swashbuckle.OData/ODataSwaggerProvider.cs
@@ -115,6 +115,8 @@ public SwaggerDocument GetSwagger(string rootUrl, string apiVersion)
 
         private SwaggerDocument MergeODataAndWebApiSwaggerDocs(string rootUrl, string apiVersion, SwaggerDocument odataSwaggerDoc)
         {
+            Contract.Requires(odataSwaggerDoc != null);
+
             var webApiSwaggerDoc = _defaultProvider.GetSwagger(rootUrl, apiVersion);
 
             webApiSwaggerDoc.paths = webApiSwaggerDoc.paths.UnionEvenIfNull(odataSwaggerDoc.paths).ToLookup(pair => pair.Key, pair => pair.Value)
@@ -140,6 +142,8 @@ private SwaggerDocument MergeODataAndWebApiSwaggerDocs(string rootUrl, string ap
 
         private PathItem CreatePathItem(IEnumerable<ApiDescription> apiDescriptions, SchemaRegistry schemaRegistry)
         {
+            Contract.Requires(apiDescriptions != null);
+
             var pathItem = new PathItem();
 
             // Group further by http method
@@ -225,6 +229,8 @@ private Operation CreateOperation(ApiDescription apiDescription, SchemaRegistry
 
         private static Parameter CreateParameter(SwaggerApiParameterDescription paramDesc, bool inPath, SchemaRegistry schemaRegistry)
         {
+            Contract.Requires(paramDesc != null);
+
             var @in = inPath
                 ? "path"
                 : MapToSwaggerParameterLocation(paramDesc.SwaggerSource);
@@ -280,5 +286,14 @@ private IEnumerable<ApiDescription> GetApiDescriptionsFor(string apiVersion)
                 ? _odataApiExplorer.ApiDescriptions 
                 : _odataApiExplorer.ApiDescriptions.Where(apiDesc => _options.VersionSupportResolver(apiDesc, apiVersion));
         }
+
+        [ContractInvariantMethod]
+        private void ObjectInvariant()
+        {
+            Contract.Invariant(_options != null);
+            Contract.Invariant(_apiVersions != null);
+            Contract.Invariant(_httpConfig != null);
+            Contract.Invariant(_odataApiExplorer != null);
+        }
     }
 }
\ No newline at end of file
diff --git a/Swashbuckle.OData/ODataSwaggerProviderOptions.cs b/Swashbuckle.OData/ODataSwaggerProviderOptions.cs
index eafd753..ed426f6 100644
--- a/Swashbuckle.OData/ODataSwaggerProviderOptions.cs
+++ b/Swashbuckle.OData/ODataSwaggerProviderOptions.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.Contracts;
 using System.Linq;
 using System.Web.Http.Description;
 using Swashbuckle.OData.Descriptions;
@@ -11,6 +12,8 @@ internal class ODataSwaggerProviderOptions
     {
         public ODataSwaggerProviderOptions(SwaggerProviderOptions swaggerProviderOptions)
         {
+            Contract.Requires(swaggerProviderOptions != null);
+
             VersionSupportResolver = swaggerProviderOptions.VersionSupportResolver;
             Schemes = swaggerProviderOptions.Schemes;
             SecurityDefinitions = swaggerProviderOptions.SecurityDefinitions;
@@ -63,6 +66,8 @@ public ODataSwaggerProviderOptions(SwaggerProviderOptions swaggerProviderOptions
 
         private static string DefaultGroupingKeySelector(ApiDescription apiDescription)
         {
+            Contract.Requires(apiDescription != null);
+
             return apiDescription.ActionDescriptor.ControllerDescriptor.ControllerName == "Restier"
                 ? ((RestierHttpActionDescriptor)apiDescription.ActionDescriptor).EntitySetName
                 : apiDescription.ActionDescriptor.ControllerDescriptor.ControllerName;
@@ -75,6 +80,8 @@ private static string DefaultSchemaIdSelector(Type type)
 
         private static ApiDescription DefaultConflictingActionsResolver(IEnumerable<ApiDescription> apiDescriptions)
         {
+            Contract.Requires(apiDescriptions != null);
+
             var first = apiDescriptions.First();
             throw new NotSupportedException($"Not supported by Swagger 2.0: Multiple operations with path '{first.RelativePathSansQueryString()}' and method '{first.HttpMethod}'. " + "See the config setting - \"ResolveConflictingActions\" for a potential workaround");
         }
diff --git a/Swashbuckle.OData/ReflectionExtensions.cs b/Swashbuckle.OData/ReflectionExtensions.cs
index 9643629..1247f92 100644
--- a/Swashbuckle.OData/ReflectionExtensions.cs
+++ b/Swashbuckle.OData/ReflectionExtensions.cs
@@ -1,4 +1,5 @@
-using System.Reflection;
+using System.Diagnostics.Contracts;
+using System.Reflection;
 
 namespace Swashbuckle.OData
 {
@@ -12,6 +13,8 @@ internal static class ReflectionExtensions
         /// <returns>The field value from the object.</returns>
         internal static T GetInstanceField<T>(this object instance, string fieldName)
         {
+            Contract.Requires(instance != null);
+
             const BindingFlags bindFlags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static;
             var field = instance.GetType().GetField(fieldName, bindFlags);
             return (T)field.GetValue(instance);
@@ -26,6 +29,9 @@ internal static T GetInstanceField<T>(this object instance, string fieldName)
         /// <returns></returns>
         internal static T InvokeFunction<T>(this object instance, string methodName)
         {
+            Contract.Requires(instance != null);
+            Contract.Requires(methodName != null);
+
             var methodInfo = instance.GetType().GetMethod(methodName, BindingFlags.NonPublic | BindingFlags.Instance);
             return (T)methodInfo.Invoke(instance, null);
         }
diff --git a/Swashbuckle.OData/SchemaRegistryExtensions.cs b/Swashbuckle.OData/SchemaRegistryExtensions.cs
index a3bc9ea..51e4aa8 100644
--- a/Swashbuckle.OData/SchemaRegistryExtensions.cs
+++ b/Swashbuckle.OData/SchemaRegistryExtensions.cs
@@ -10,6 +10,7 @@ internal static class SchemaRegistryExtensions
     {
         public static Schema GetOrRegisterODataType(this SchemaRegistry registry, Type type)
         {
+            Contract.Requires(registry != null);
             Contract.Requires(type != null);
 
             var isAGenericODataType = IsAGenericODataType(type);
@@ -20,6 +21,8 @@ public static Schema GetOrRegisterODataType(this SchemaRegistry registry, Type t
 
         private static bool IsAGenericODataType(Type type)
         {
+            Contract.Requires(type != null);
+
             var isDelta = type.IsGenericType && type.GetGenericTypeDefinition() == typeof (Delta<>);
             var isSingleResult = type.IsGenericType && type.GetGenericTypeDefinition() == typeof (SingleResult<>);
 
diff --git a/Swashbuckle.OData/Swashbuckle.OData.csproj b/Swashbuckle.OData/Swashbuckle.OData.csproj
index b75a38f..1b58951 100644
--- a/Swashbuckle.OData/Swashbuckle.OData.csproj
+++ b/Swashbuckle.OData/Swashbuckle.OData.csproj
@@ -38,16 +38,16 @@
     <CodeContractsAssertsToContractsCheckBox>True</CodeContractsAssertsToContractsCheckBox>
     <CodeContractsRedundantTests>True</CodeContractsRedundantTests>
     <CodeContractsMissingPublicRequiresAsWarnings>True</CodeContractsMissingPublicRequiresAsWarnings>
-    <CodeContractsMissingPublicEnsuresAsWarnings>False</CodeContractsMissingPublicEnsuresAsWarnings>
+    <CodeContractsMissingPublicEnsuresAsWarnings>True</CodeContractsMissingPublicEnsuresAsWarnings>
     <CodeContractsInferRequires>True</CodeContractsInferRequires>
     <CodeContractsInferEnsures>False</CodeContractsInferEnsures>
     <CodeContractsInferEnsuresAutoProperties>True</CodeContractsInferEnsuresAutoProperties>
     <CodeContractsInferObjectInvariants>False</CodeContractsInferObjectInvariants>
     <CodeContractsSuggestAssumptions>False</CodeContractsSuggestAssumptions>
     <CodeContractsSuggestAssumptionsForCallees>False</CodeContractsSuggestAssumptionsForCallees>
-    <CodeContractsSuggestRequires>False</CodeContractsSuggestRequires>
+    <CodeContractsSuggestRequires>True</CodeContractsSuggestRequires>
     <CodeContractsNecessaryEnsures>True</CodeContractsNecessaryEnsures>
-    <CodeContractsSuggestObjectInvariants>False</CodeContractsSuggestObjectInvariants>
+    <CodeContractsSuggestObjectInvariants>True</CodeContractsSuggestObjectInvariants>
     <CodeContractsSuggestReadonly>True</CodeContractsSuggestReadonly>
     <CodeContractsRunInBackground>True</CodeContractsRunInBackground>
     <CodeContractsShowSquigglies>True</CodeContractsShowSquigglies>