Null check changeEvent.contentChanges[0] and log bad messages

Author: rjmholt

src/features/HelpCompletion.ts

@@ -44,7 +44,7 @@ export class HelpCompletionFeature implements IFeature {
     }
 
     public onEvent(changeEvent: TextDocumentChangeEvent): void {
-        if (!changeEvent) {
+        if (!(changeEvent && changeEvent.contentChanges && changeEvent.contentChanges[0])) {
             return;
         }