Fix missing feild value in Metadata Editor

The latest release of JupyterLab updated to the latest release
of blueprintjs core, which included an async bugfix for
`InputGroup` which broke how our async update interacts with fields.
Causing any already rendered `InputGroup` to not update it value
on an async call to `uodate()` such as the one we do after calling
the metadata api.

I solved this by making the rendering of the display_name field
conditional on the existance of an inital value, just like we
already do with the other fields.

Fixes elyra-ai#883

packages/metadata-common/src/MetadataEditor.tsx

@@ -216,9 +216,9 @@ export class MetadataEditor extends ReactWidget {
     this.handleDirtyState(true);
     // Special case because all metadata has a display name
     if (schemaField === 'display_name') {
-      this.displayName = event.nativeEvent.srcElement.value;
+      this.displayName = event.nativeEvent.target.value;
     } else {
-      this.metadata[schemaField] = event.nativeEvent.srcElement.value;
+      this.metadata[schemaField] = event.nativeEvent.target.value;
     }
   }
 
@@ -450,15 +450,17 @@ export class MetadataEditor extends ReactWidget {
     return (
       <div className={ELYRA_METADATA_EDITOR_CLASS}>
         <h3> {headerText} </h3>
-        {this.renderTextInput(
-          'Name',
-          '',
-          'display_name',
-          this.displayName,
-          '(required)',
-          false,
-          intent
-        )}
+        {this.displayName
+          ? this.renderTextInput(
+              'Name',
+              '',
+              'display_name',
+              this.displayName,
+              '(required)',
+              false,
+              intent
+            )
+          : null}
         {inputElements}
         <FormGroup className={'elyra-metadataEditor-saveButton'}>
           <Button