move check to validation and add test coverage

packages/concerto-core/lib/serializer/jsongenerator.js

@@ -85,9 +85,6 @@ class JSONGenerator {
      */
     visitMapDeclaration(mapDeclaration, parameters) {
         const obj = parameters.stack.pop();
-        if (!((obj instanceof Map))) {
-            throw new Error('Expected a Map, but found ' + obj);
-        }
         return Object.fromEntries(obj);
     }
 

packages/concerto-core/lib/serializer/resourcevalidator.js

@@ -117,6 +117,10 @@ class ResourceValidator {
 
         const obj = parameters.stack.pop();
 
+        if (!((obj instanceof Map))) {
+            throw new Error('Expected a Map, but found ' + obj);
+        }
+
         obj.forEach((key,value) => {
             if(!ModelUtil.isSystemProperty(key)) {
                 if (typeof key !== 'string') {

packages/concerto-core/test/serializer.js

@@ -261,6 +261,18 @@ describe('Serializer', () => {
             });
         });
 
+        it('should throw if the value for a map is not a Map instance', () => {
+            let address = factory.newConcept('org.acme.sample', 'Address');
+            address.city = 'Winchester';
+            address.country = 'UK';
+            address.elevation = 3.14;
+            address.postcode = 'SO21 2JN';
+            address.testMap = 'xyz'; // bad value
+            (() => {
+                serializer.toJSON(address);
+            }).should.throw(Error, /Expected a Map, but found xyz/);
+        });
+
         it('should generate a field if an empty string is specififed', () => {
             let resource = factory.newResource('org.acme.sample', 'SampleAsset', '1');
             resource.owner = factory.newRelationship('org.acme.sample', 'SampleParticipant', '[email protected]');