title: Added ng-select reactive form validation messages not showing
body: <p>I added an error message to ng-select component to show error messages when it's dirty and value not selected. But the error message is not showing. But the validation is working.</p>
  
  <p><a href="https://ng-select.github.io/ng-select/" rel="nofollow noreferrer">https://ng-select.github.io/ng-select/</a></p>
  
  <pre><code>&lt;form [formGroup]="itemForm" (ngSubmit)=onSubmitForm()&gt;
      &lt;div class="form-group col"&gt;
          &lt;label for="pack_size"&gt;Supplier&lt;/label&gt;
          &lt;ng-select 
              bindLabel="supplier" 
              placeholder="Select Supplier" 
              formControlName="supplier"
              [ngClass]="{ 'is-invalid': supplier.invalid &amp;&amp; supplier.touched }" 
              &gt;
              &lt;ng-option *ngFor="let supplier of suppliers" [value]="supplier.id"&gt;
                  {{supplier.description}}
              &lt;/ng-option&gt;
          &lt;/ng-select&gt;
          &lt;div *ngIf="supplier.invalid &amp;&amp; supplier.touched" class="invalid-feedback"&gt;
              &lt;div *ngIf="!!supplier.errors.required"&gt;Supplier is required&lt;/div&gt;
          &lt;/div&gt;
      &lt;/div&gt;
      &lt;/div&gt;
      &lt;button class="btn btn-primary" type="submit"
                              [disabled]="itemForm.invalid"&gt;Add&lt;/button&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>CSS classes that has been added</p>
  
  <pre><code>ng-select.ng-invalid.ng-touched .ng-select-container {
      border-color: #dc3545;
      box-shadow: inset 0 1px 1px rgba(0, 0, 0, 0.075), 0 0 0 3px #fde6e8;
  }
  </code></pre>
  
  <p>ts file for the form functions as requested</p>
  
  <pre><code>itemForm: FormGroup;
  
  constructor(
      private _fb: FormBuilder,
  ) {}
  
  ngOnInit() {
      this.submitted = false;
      this.buttonValue = 'Add';
      this.loadOthers();
      this.itemsLoad();
      this.itemForm = this._fb.group({
          id: [null],
          name: [null, Validators.required],
          pack_type: [null, Validators.required],
          pack_size: [null, Validators.required],
          supplier: [null, Validators.required],
          item_category: [null, Validators.required],
      });
  }
  
  
  get id() {
      return this.itemForm.get('id');
  }
  
  get name() {
      return this.itemForm.get('name');
  }
  
  get pack_type() {
      return this.itemForm.get('pack_type');
  }
  
  get pack_size() {
      return this.itemForm.get('pack_size');
  }
  
  get supplier() {
      return this.itemForm.get('supplier');
  }
  
  get item_category() {
      return this.itemForm.get('item_category');
  }
  </code></pre>