feat(typeahead): show results when typeaheadMinLength is 0 and the se…

…arch string is empty (#2352)

* Update typeahead.directive.ts

* Update typeahead.directive.ts

src/typeahead/typeahead.directive.ts

@@ -129,7 +129,7 @@ export class TypeaheadDirective implements OnInit, OnDestroy {
       : e.target.textContent !== undefined
         ? e.target.textContent
         : e.target.innerText;
-    if (value && value.trim().length >= this.typeaheadMinLength) {
+    if (value != null && value.trim().length >= this.typeaheadMinLength) {
       this.typeaheadLoading.emit(true);
       this.keyUpEventEmitter.emit(e.target.value);
     } else {