diff --git a/RDFSharp.Test/Store/Engines/RDFMemoryStoreTest.cs b/RDFSharp.Test/Store/Engines/RDFMemoryStoreTest.cs
index 6b0c9c9f..83f5ec5d 100644
--- a/RDFSharp.Test/Store/Engines/RDFMemoryStoreTest.cs
+++ b/RDFSharp.Test/Store/Engines/RDFMemoryStoreTest.cs
@@ -1676,7 +1676,7 @@ public void ShouldRaiseExceptionOnImportingFromDataTableHavingRowWithNullObjectA
         [TestMethod]
         public void ShouldImportFromUri()
         {
-            RDFMemoryStore store = RDFMemoryStore.FromUri(new Uri("https://w3c.github.io/rdf-tests/nquads/nq-syntax-uri-01.nq"));
+            RDFMemoryStore store = RDFMemoryStore.FromUri(new Uri("https://w3c.github.io/rdf-tests/rdf/rdf11/rdf-n-quads/nq-syntax-uri-01.nq"));
 
             Assert.IsNotNull(store);
             Assert.IsTrue(store.QuadruplesCount > 0);
@@ -1693,7 +1693,7 @@ public void ShouldRaiseExceptionOnImportingFromRelativeUri()
         [TestMethod]
         public async Task ShouldImportFromUriAsync()
         {
-            RDFMemoryStore store = await RDFMemoryStore.FromUriAsync(new Uri("https://w3c.github.io/rdf-tests/nquads/nq-syntax-uri-01.nq"));
+            RDFMemoryStore store = await RDFMemoryStore.FromUriAsync(new Uri("https://w3c.github.io/rdf-tests/rdf/rdf11/rdf-n-quads/nq-syntax-uri-01.nq"));
 
             Assert.IsNotNull(store);
             Assert.IsTrue(store.QuadruplesCount > 0);
diff --git a/RDFSharp/Query/Mirella/Algebra/RDFPattern.cs b/RDFSharp/Query/Mirella/Algebra/RDFPattern.cs
index 10d000d0..97114f4f 100644
--- a/RDFSharp/Query/Mirella/Algebra/RDFPattern.cs
+++ b/RDFSharp/Query/Mirella/Algebra/RDFPattern.cs
@@ -69,6 +69,7 @@ public class RDFPattern : RDFPatternGroupMember
         /// </summary>
         public RDFPattern(RDFPatternMember subject, RDFPatternMember predicate, RDFPatternMember objLit)
         {
+            #region Guards
             if (subject == null)
                 throw new RDFQueryException("Cannot create RDFPattern because given \"subject\" parameter is null");
             if (!(subject is RDFResource || subject is RDFVariable))
@@ -83,6 +84,7 @@ public RDFPattern(RDFPatternMember subject, RDFPatternMember predicate, RDFPatte
                 throw new RDFQueryException("Cannot create RDFPattern because given \"objLit\" parameter is null");
             if (!(objLit is RDFResource || objLit is RDFLiteral || objLit is RDFVariable))
                 throw new RDFQueryException("Cannot create RDFPattern because given \"objLit\" parameter (" + objLit + ") is neither a resource, or a literal or a variable");
+            #endregion
 
             Variables = new List<RDFVariable>();
             IsEvaluable = true;
@@ -91,27 +93,18 @@ public RDFPattern(RDFPatternMember subject, RDFPatternMember predicate, RDFPatte
             
             //Subject
             Subject = subject;
-            if (subject is RDFVariable)
-            {
-                if (!Variables.Any(v => v.Equals(subject)))
-                    Variables.Add((RDFVariable)subject);
-            }
+            if (subject is RDFVariable subjVar && !Variables.Any(v => v.Equals(subjVar)))
+                Variables.Add(subjVar);
 
             //Predicate
             Predicate = predicate;
-            if (predicate is RDFVariable)
-            {
-                if (!Variables.Any(v => v.Equals(predicate)))
-                    Variables.Add((RDFVariable)predicate);
-            }
+            if (predicate is RDFVariable predVar && !Variables.Any(v => v.Equals(predVar)))
+                Variables.Add(predVar);
 
             //Object/Literal
             Object = objLit;
-            if (objLit is RDFVariable)
-            {
-                if (!Variables.Any(v => v.Equals(objLit)))
-                    Variables.Add((RDFVariable)objLit);
-            }
+            if (objLit is RDFVariable objVar && !Variables.Any(v => v.Equals(objVar)))
+                Variables.Add(objVar);
         }
 
         /// <summary>
@@ -119,18 +112,17 @@ public RDFPattern(RDFPatternMember subject, RDFPatternMember predicate, RDFPatte
         /// </summary>
         public RDFPattern(RDFPatternMember context, RDFPatternMember subject, RDFPatternMember predicate, RDFPatternMember objLit) : this(subject, predicate, objLit)
         {
+            #region Guards
             if (context == null)
                 throw new RDFQueryException("Cannot create RDFPattern because given \"context\" parameter is null");
             if (!(context is RDFContext || context is RDFVariable))
                 throw new RDFQueryException("Cannot create RDFPattern because given \"context\" parameter (" + context + ") is neither a context or a variable");
+            #endregion
 
             //Context
             Context = context;
-            if (context is RDFVariable)
-            {
-                if (!Variables.Any(v => v.Equals(context)))
-                    Variables.Add((RDFVariable)context);
-            }
+            if (context is RDFVariable ctxVar && !Variables.Any(v => v.Equals(ctxVar)))
+                Variables.Add(ctxVar);
         }
         #endregion
 
diff --git a/RDFSharp/Query/Mirella/Algebra/RDFPatternGroup.cs b/RDFSharp/Query/Mirella/Algebra/RDFPatternGroup.cs
index 6c22aaaf..5677705c 100644
--- a/RDFSharp/Query/Mirella/Algebra/RDFPatternGroup.cs
+++ b/RDFSharp/Query/Mirella/Algebra/RDFPatternGroup.cs
@@ -64,19 +64,13 @@ public RDFPatternGroup()
         /// List-ctor to build a named pattern group with the given list of patterns
         /// </summary>
         public RDFPatternGroup(List<RDFPattern> patterns) : this()
-        {
-            if (patterns != null)
-                patterns.ForEach(p => AddPattern(p));
-        }
+            => patterns?.ForEach(p => AddPattern(p));
 
         /// <summary>
         /// List-ctor to build a named pattern group with the given list of patterns and filters
         /// </summary>
         public RDFPatternGroup(List<RDFPattern> patterns, List<RDFFilter> filters) : this(patterns)
-        {
-            if (filters != null)
-                filters.ForEach(f => AddFilter(f));
-        }
+            => filters?.ForEach(f => AddFilter(f));
         #endregion
 
         #region Interfaces