Merge remote-tracking branch 'origin/master'

frontend/src/app/validators/keywords.validator.ts

@@ -1,7 +1,7 @@
 import {AbstractControl} from '@angular/forms';
 
 export function keywordsValidator(control: AbstractControl): { [key: string]: any } | null {
-  if (control.value === undefined) {
+  if (control.value === null) {
     return null;
   }
   let split: string[];