diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3b0625d..a8793a8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,12 @@
 This log documents significant changes for each release.  This project follows
 [Semantic Versioning](http://semver.org/).
 
+## [2.14.5] - 2022-06-07
+### Added
+- Version number to fhirpath.js demo page.
+### Fixed
+- "extension()" for primitive types did not work properly without a value.
+
 ## [2.14.4] - 2022-05-23
 ### Added
 - Suite of performance tests.
diff --git a/demo/public/app.js b/demo/public/app.js
index aa07495..9f80df1 100644
--- a/demo/public/app.js
+++ b/demo/public/app.js
@@ -13,6 +13,8 @@ require("codemirror/lib/codemirror.css");
 
 const example = require("json-loader!yaml-loader!./patient-example.yaml");
 
+document.getElementById('version').innerText = '(version ' + fhirpath.version + ')';
+
 const debounce = (func, delay) => {
   let inDebounce;
   return () => {
diff --git a/demo/public/index.html b/demo/public/index.html
index 82c1148..122d014 100644
--- a/demo/public/index.html
+++ b/demo/public/index.html
@@ -2,6 +2,7 @@
 <html>
   <head>
     <meta charset="utf-8">
+    <meta http-equiv="X-UA-Compatible" content="IE=edge">
     <!-- <link rel="stylesheet" href="app.css"> -->
     <title>fhirpath.js Demo</title>
     <!-- anti-clickjacking script from:
@@ -21,6 +22,7 @@
       <div id="header">
         A demo of the
         <a href="https://github.com/HL7/fhirpath.js">fhirpath.js</a>
+        <span id="version"></span>
         JavaScript Engine for HL7 FHIRPath
       </div>
       <input id="path"
diff --git a/package-lock.json b/package-lock.json
index ec3f655..20c9798 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "fhirpath",
-  "version": "2.14.4",
+  "version": "2.14.5",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "fhirpath",
-      "version": "2.14.4",
+      "version": "2.14.5",
       "license": "MIT",
       "dependencies": {
         "@lhncbc/ucum-lhc": "^4.1.3",
diff --git a/package.json b/package.json
index ae904a9..479f02e 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "fhirpath",
-  "version": "2.14.4",
+  "version": "2.14.5",
   "description": "A FHIRPath engine",
   "main": "src/fhirpath.js",
   "dependencies": {
diff --git a/src/fhirpath.js b/src/fhirpath.js
index aabb9e2..49636c5 100644
--- a/src/fhirpath.js
+++ b/src/fhirpath.js
@@ -336,21 +336,18 @@ engine.MemberInvocation = function(ctx, parentData, node ) {
           // Use actualTypes to find the field's value
           for (let t of actualTypes) {
             let field = key + t;
-            toAdd = res.data[field];
-            if (toAdd !== undefined) {
+            toAdd = res.data?.[field];
+            _toAdd = res.data?.['_' + field];
+            if (toAdd !== undefined || _toAdd !== undefined) {
               childPath = t;
-              _toAdd = res.data['_' + key];
               break;
-            } else {
-              toAdd = res._data[key];
             }
           }
         }
         else {
-          toAdd = res.data[key];
-          if (toAdd !== undefined) {
-            _toAdd = res.data['_' + key];
-          } else {
+          toAdd = res.data?.[key];
+          _toAdd = res.data?.['_' + key];
+          if (toAdd === undefined && _toAdd === undefined) {
             toAdd = res._data[key];
           }
           if (key === 'extension') {
@@ -358,7 +355,7 @@ engine.MemberInvocation = function(ctx, parentData, node ) {
           }
         }
 
-        if (util.isSome(toAdd)) {
+        if (util.isSome(toAdd) || util.isSome(_toAdd)) {
           if(Array.isArray(toAdd)) {
             acc = acc.concat(toAdd.map((x, i)=>
               makeResNode(x, childPath, _toAdd && _toAdd[i])));
diff --git a/src/types.js b/src/types.js
index 6603bfe..01bcebf 100644
--- a/src/types.js
+++ b/src/types.js
@@ -984,7 +984,7 @@ class ResourceNode {
   constructor(data, path, _data) {
     // If data is a resource (maybe a contained resource) reset the path
     // information to the resource type.
-    if (data.resourceType)
+    if (data?.resourceType)
       path = data.resourceType;
     this.path = path;
     this.data = getResourceNodeData(data, path);
@@ -1021,7 +1021,7 @@ class ResourceNode {
  * @return {FP_Quantity|Object|...}
  */
 function getResourceNodeData(data, path) {
-  if (path === 'Quantity' && data.system === ucumSystemUrl) {
+  if (path === 'Quantity' && data?.system === ucumSystemUrl) {
     if (typeof data.value === 'number' && typeof data.code === 'string') {
       data = new FP_Quantity(data.value, FP_Quantity.mapUCUMCodeToTimeUnits[data.code] || '\'' + data.code + '\'');
     }
diff --git a/test/benchmark.js b/test/benchmark.js
index b56a7ab..363febe 100644
--- a/test/benchmark.js
+++ b/test/benchmark.js
@@ -15,13 +15,39 @@ const { spawn } = require('child_process');
 const myArgs = process.argv.slice(2);
 const prevVersion = myArgs.length === 1 ? '@' + myArgs[0] : '@latest';
 
+const benny = require('benny');
+const open = require('open');
+const current_fhirpath = require('../src/fhirpath');
+const current_r4_model = require('../fhir-context/r4');
+const minimumDataset = require('./resources/Minimum-Data-Set---version-3.0.R4.json');
+const currentVersion = require('../package.json').version;
+
+
 const child = spawn('npm', ['i','--prefix', './test/benchmark/prev-fhirpath', 'fhirpath' + prevVersion], {
   stdio: 'inherit'
 });
 
 child.on('exit', code => {
   if (code === 0) {
+    const previous_fhirpath = require('./benchmark/prev-fhirpath/node_modules/fhirpath');
+    const previous_r4_model = require('./benchmark/prev-fhirpath/node_modules/fhirpath/fhir-context/r4');
+    const previousVersion = require('./benchmark/prev-fhirpath/node_modules/fhirpath/package.json').version;
     // Insert performance test suites here:
-    require('./benchmark/intersect');
+    [
+      'intersect',
+      'member-invocation'
+    ].forEach(filename => {
+      require('./benchmark/'+ filename)({
+        benny,
+        open,
+        previous_fhirpath,
+        previous_r4_model,
+        current_fhirpath,
+        current_r4_model,
+        minimumDataset,
+        currentVersion,
+        previousVersion
+      })
+    })
   }
 });
diff --git a/test/benchmark/intersect.js b/test/benchmark/intersect.js
index 936b2d4..3366cbe 100644
--- a/test/benchmark/intersect.js
+++ b/test/benchmark/intersect.js
@@ -1,88 +1,89 @@
-const b = require('benny');
-const open = require('open');
-
-const previous_fhirpath = require('./prev-fhirpath/node_modules/fhirpath');
-const previous_r4_model = require('./prev-fhirpath/node_modules/fhirpath/fhir-context/r4');
-const current_fhirpath = require('../../src/fhirpath');
-const current_r4_model = require('../../fhir-context/r4');
 const _ = require('lodash');
 
-const minimumDataset = require('../resources/Minimum-Data-Set---version-3.0.R4.json');
-
-const bigItems = current_fhirpath.evaluate(minimumDataset,'repeat(item)', {},  current_r4_model);
-const bigItemsCopy = _.cloneDeep(bigItems);
-const numberOfBigItems = current_fhirpath.evaluate({}, '%items.count()', { items: bigItems }, current_r4_model)[0];
+module.exports = ({
+                    benny,
+                    open,
+                    previous_fhirpath,
+                    previous_r4_model,
+                    current_fhirpath,
+                    current_r4_model,
+                    minimumDataset,
+                    currentVersion,
+                    previousVersion
+                  }) => {
 
-const smallItems = current_fhirpath.evaluate(minimumDataset,'repeat(item).repeat(code)', {},  current_r4_model);
-const smallItemsCopy = _.cloneDeep(smallItems);
-const numberOfSmallItems = current_fhirpath.evaluate({}, '%items.count()', { items: smallItems }, current_r4_model)[0];
+  const bigItems = current_fhirpath.evaluate(minimumDataset,'repeat(item)', {},  current_r4_model);
+  const bigItemsCopy = _.cloneDeep(bigItems);
+  const numberOfBigItems = current_fhirpath.evaluate({}, '%items.count()', { items: bigItems }, current_r4_model)[0];
 
-const previousVersion = require('./prev-fhirpath/node_modules/fhirpath/package.json').version;
-const currentVersion = require('../../package.json').version;
+  const smallItems = current_fhirpath.evaluate(minimumDataset,'repeat(item).repeat(code)', {},  current_r4_model);
+  const smallItemsCopy = _.cloneDeep(smallItems);
+  const numberOfSmallItems = current_fhirpath.evaluate({}, '%items.count()', { items: smallItems }, current_r4_model)[0];
 
-const expression = '%items.intersect(%itemsCopy)';
+  const expression = '%items.intersect(%itemsCopy)';
 
-const cases = [
-  {
-    name: `${numberOfBigItems} big items using evaluate()`,
-    testFunction: (fhirpath, model) => {
-      fhirpath.evaluate({}, expression, { items: bigItems, itemsCopy: bigItemsCopy }, model);
-    }
-  },
-  {
-    name: `${numberOfBigItems} big items using compile()`,
-    testFunction: (fhirpath, model, compiledFn) => {
-      compiledFn({}, { items: bigItems, itemsCopy: bigItemsCopy });
-    }
-  },
-  {
-    name: `${numberOfSmallItems} small items using evaluate()`,
-    testFunction: (fhirpath, model) => {
-      fhirpath.evaluate({}, expression, { items: smallItems, itemsCopy: smallItemsCopy }, model);
-    }
-  },
-  {
-    name: `${numberOfSmallItems} small items using compile()`,
-    testFunction: (fhirpath, model, compiledFn) => {
-      compiledFn({}, { items: smallItems, itemsCopy: smallItemsCopy });
+  const cases = [
+    {
+      name: `${numberOfBigItems} big items using evaluate()`,
+      testFunction: (fhirpath, model) => {
+        fhirpath.evaluate({}, expression, { items: bigItems, itemsCopy: bigItemsCopy }, model);
+      }
+    },
+    {
+      name: `${numberOfBigItems} big items using compile()`,
+      testFunction: (fhirpath, model, compiledFn) => {
+        compiledFn({}, { items: bigItems, itemsCopy: bigItemsCopy });
+      }
+    },
+    {
+      name: `${numberOfSmallItems} small items using evaluate()`,
+      testFunction: (fhirpath, model) => {
+        fhirpath.evaluate({}, expression, { items: smallItems, itemsCopy: smallItemsCopy }, model);
+      }
+    },
+    {
+      name: `${numberOfSmallItems} small items using compile()`,
+      testFunction: (fhirpath, model, compiledFn) => {
+        compiledFn({}, { items: smallItems, itemsCopy: smallItemsCopy });
+      }
     }
-  }
-].reduce((arr, item) => {
-  arr.push(
-    b.add(
-      `${item.name} [${previousVersion}]`,
-      item.testFunction.bind(
-        this,
-        previous_fhirpath,
-        previous_r4_model,
-        previous_fhirpath.compile(expression, previous_r4_model)
+  ].reduce((arr, item) => {
+    arr.push(
+      benny.add(
+        `${item.name} [${previousVersion}]`,
+        item.testFunction.bind(
+          this,
+          previous_fhirpath,
+          previous_r4_model,
+          previous_fhirpath.compile(expression, previous_r4_model)
+        )
       )
-    )
-  );
-  arr.push(
-    b.add(
-      `${item.name} [${currentVersion}]`,
-      item.testFunction.bind(
-        this,
-        current_fhirpath,
-        current_r4_model,
-        current_fhirpath.compile(expression, current_r4_model)
+    );
+    arr.push(
+      benny.add(
+        `${item.name} [${currentVersion}]`,
+        item.testFunction.bind(
+          this,
+          current_fhirpath,
+          current_r4_model,
+          current_fhirpath.compile(expression, current_r4_model)
+        )
       )
-    )
-  );
-  return arr;
-}, []);
+    );
+    return arr;
+  }, []);
 
-b.suite(
-  'intersect() of two collections with',
-  ...cases,
-  b.cycle(),
-  b.complete(),
-  b.configure({
-    minDisplayPrecision: 2
-  }),
-  b.save({ file: 'intersect', folder: __dirname + '/results', version: currentVersion }),
-  b.save({ file: 'intersect', folder: __dirname + '/results', format: 'chart.html' }),
-).then(() => {
-  open(__dirname + '/results/intersect.chart.html');
-});
+  benny.suite(
+    'intersect() of two collections with',
+    ...cases,
+    benny.cycle(),
+    benny.complete(),
+    benny.configure({
+      minDisplayPrecision: 2
+    }),
+    benny.save({ file: 'intersect', folder: __dirname + '/results', version: currentVersion }),
+    benny.save({ file: 'intersect', folder: __dirname + '/results', format: 'chart.html' }),
+  ).then(() => {
+    open(__dirname + '/results/intersect.chart.html');
+  });
+}
diff --git a/test/benchmark/member-invocation.js b/test/benchmark/member-invocation.js
new file mode 100644
index 0000000..60f1cb3
--- /dev/null
+++ b/test/benchmark/member-invocation.js
@@ -0,0 +1,70 @@
+const _ = require('lodash');
+
+module.exports = ({
+                    benny,
+                    open,
+                    previous_fhirpath,
+                    previous_r4_model,
+                    current_fhirpath,
+                    current_r4_model,
+                    minimumDataset,
+                    currentVersion,
+                    previousVersion
+                  }) => {
+
+  const numberOfItems = current_fhirpath.evaluate(minimumDataset,'Questionnaire.item.count()', {},  current_r4_model);
+  const expression = 'Questionnaire.item';
+
+  const cases = [
+    {
+      name: `using evaluate()`,
+      testFunction: (fhirpath, model) => {
+        fhirpath.evaluate(minimumDataset, expression, {}, model);
+      }
+    },
+    {
+      name: `using compile()`,
+      testFunction: (fhirpath, model, compiledFn) => {
+        compiledFn(minimumDataset, {});
+      }
+    }
+  ].reduce((arr, item) => {
+    arr.push(
+      benny.add(
+        `${item.name} [${previousVersion}]`,
+        item.testFunction.bind(
+          this,
+          previous_fhirpath,
+          previous_r4_model,
+          previous_fhirpath.compile(expression, previous_r4_model)
+        )
+      )
+    );
+    arr.push(
+      benny.add(
+        `${item.name} [${currentVersion}]`,
+        item.testFunction.bind(
+          this,
+          current_fhirpath,
+          current_r4_model,
+          current_fhirpath.compile(expression, current_r4_model)
+        )
+      )
+    );
+    return arr;
+  }, []);
+
+  benny.suite(
+    `Getting ${numberOfItems} items with engine.MemberInvocation`,
+    ...cases,
+    benny.cycle(),
+    benny.complete(),
+    benny.configure({
+      minDisplayPrecision: 2
+    }),
+    benny.save({ file: 'member-invocation', folder: __dirname + '/results', version: currentVersion }),
+    benny.save({ file: 'member-invocation', folder: __dirname + '/results', format: 'chart.html' }),
+  ).then(() => {
+    open(__dirname + '/results/member-invocation.chart.html');
+  });
+}
diff --git a/test/cases/extensions.yaml b/test/cases/extensions.yaml
index 740cf56..34719c9 100644
--- a/test/cases/extensions.yaml
+++ b/test/cases/extensions.yaml
@@ -60,6 +60,21 @@ tests:
       result:
         - true
 
+    - desc: '** expression with extension() for primitive type (without using FHIR model data) when only extension is present'
+      inputfile: patient-example-2.json
+      expression: >-
+        Patient.communication.preferred.extension('test').exists()
+      result:
+        - true
+
+    - desc: '** expression with extension() for primitive type (using FHIR model data) when only extension is present'
+      inputfile: patient-example-2.json
+      model: r4
+      expression: >-
+        Patient.communication.preferred.extension('test').value.id
+      result:
+        - testing
+
     - desc: '** expression with extension() for primitive type (using FHIR model data)'
       inputfile: patient-example.json
       model: r4
diff --git a/test/resources/patient-example-2.json b/test/resources/patient-example-2.json
new file mode 100644
index 0000000..1947ac1
--- /dev/null
+++ b/test/resources/patient-example-2.json
@@ -0,0 +1,26 @@
+{
+  "resourceType": "Patient",
+  "communication": [
+    {
+      "language": {
+        "coding": [
+          {
+            "system": "urn:ietf:bcp:47",
+            "code": "nl",
+            "display": "Dutch"
+          }
+        ]
+      },
+      "_preferred": {
+        "extension": [
+          {
+            "url": "test",
+            "_valueString": {
+              "id": "testing"
+            }
+          }
+        ]
+      }
+    }
+  ]
+}
