fix #1067 UI sends wrong request when creating new metadata field without qualifier

src/app/core/registry/registry.service.spec.ts

@@ -326,6 +326,25 @@ describe('RegistryService', () => {
     });
   });
 
+  describe('when createMetadataField is called with a blank qualifier', () => {
+    let result: Observable<MetadataField>;
+    let metadataField: MetadataField;
+
+    beforeEach(() => {
+      metadataField = mockFieldsList[0];
+      metadataField.qualifier = '';
+      result = registryService.createMetadataField(metadataField, mockSchemasList[0]);
+    });
+
+    it('should return the created metadata field with a null qualifier', (done) => {
+      metadataField.qualifier = null;
+      result.subscribe((field: MetadataField) => {
+        expect(field).toEqual(metadataField);
+        done();
+      });
+    });
+  });
+
   describe('when updateMetadataField is called', () => {
     let result: Observable<MetadataField>;
 
@@ -341,6 +360,25 @@ describe('RegistryService', () => {
     });
   });
 
+  describe('when updateMetadataField is called with a blank qualifier', () => {
+    let result: Observable<MetadataField>;
+    let metadataField: MetadataField;
+
+    beforeEach(() => {
+      metadataField = mockFieldsList[0];
+      metadataField.qualifier = '';
+      result = registryService.updateMetadataField(metadataField);
+    });
+
+    it('should return the updated metadata field with a null qualifier', (done) => {
+      metadataField.qualifier = null;
+      result.subscribe((field: MetadataField) => {
+        expect(field).toEqual(metadataField);
+        done();
+      });
+    });
+  });
+
   describe('when deleteMetadataSchema is called', () => {
     let result: Observable<RemoteData<NoContent>>;
 

src/app/core/registry/registry.service.ts

@@ -245,6 +245,9 @@ export class RegistryService {
    * @param schema   The MetadataSchema to create the field in
    */
   public createMetadataField(field: MetadataField, schema: MetadataSchema): Observable<MetadataField> {
+    if (!field.qualifier) {
+      field.qualifier = null;
+    }
     return this.metadataFieldService.create(field, new RequestParam('schemaId', schema.id)).pipe(
       getFirstSucceededRemoteDataPayload(),
       hasValueOperator(),
@@ -260,6 +263,9 @@ export class RegistryService {
    * @param field    The MetadataField to update
    */
   public updateMetadataField(field: MetadataField): Observable<MetadataField> {
+    if (!field.qualifier) {
+      field.qualifier = null;
+    }
     return this.metadataFieldService.put(field).pipe(
       getFirstSucceededRemoteDataPayload(),
       hasValueOperator(),