fix: ignore null properties

rules/utils/element.js

@@ -1,6 +1,7 @@
 const {
   isArray,
   isDefined,
+  isNil,
   some
 } = require('min-dash');
 
@@ -147,7 +148,7 @@ module.exports.hasProperties = function(node, properties, parentNode = null) {
       ];
     }
 
-    if (propertyChecks.allowed === false && isDefined(propertyValue)) {
+    if (propertyChecks.allowed === false && isDefined(propertyValue) && !isNil(propertyValue)) {
       return [
         ...results,
         {

test/helper.js

@@ -99,7 +99,7 @@ function createElement(type, properties) {
   };
 
   const setParent = (property) => {
-    if (property.$type) {
+    if (property && property.$type) {
       const childModdleElement = property;
 
       childModdleElement.$parent = moddleElement;

test/utils/element.spec.js

@@ -456,7 +456,7 @@ describe('utils/element', function() {
 
     describe('allowed', function() {
 
-      it('should not return errors', function() {
+      it('should not return errors (undefined)', function() {
 
         // given
         const serviceTask = createElement('bpmn:ServiceTask');
@@ -473,6 +473,25 @@ describe('utils/element', function() {
       });
 
 
+      it('should not return errors (null)', function() {
+
+        // given
+        const serviceTask = createElement('bpmn:ServiceTask', {
+          modelerTemplate: null
+        });
+
+        // when
+        const errors = hasProperties(serviceTask, {
+          modelerTemplate: {
+            allowed: false
+          }
+        });
+
+        // then
+        expect(errors).to.be.empty;
+      });
+
+
       it('should return errors', function() {
 
         // given