title: ng-multiselect-dropdown onDeSelectAll() not working
body: <p>I am using ng-multiselect dropdown in my angular code. While all the onSelect, onSelectAll, onDeSelect methods are working fine, onDeselctAll method doesn't receive the array of items deselected. I checked in the official site but it was of no use : <a href="https://www.npmjs.com/package/ng-multiselect-dropdown" rel="noreferrer">https://www.npmjs.com/package/ng-multiselect-dropdown</a>. 
  Any idea where I might be going wrong? PFB the code snippet:</p>
  
  <p><strong>.html file</strong></p>
  
  <pre><code>&lt;ng-multiselect-dropdown *ngIf="filteredSids.length &gt; 0"
                                               [data]="filteredSids"
                                               [disabled]="false"
                                               [(ngModel)]="selectedSids"
                                               (onSelect)="selectedSIDs($event); onItemSelect($event)"
                                               (onSelectAll)="onSelectAll($event)"
                                               (onDeSelect)="onItemDeSelect($event)"
                                               (onDeSelectAll)="onDeSelectAll($event)"
                                               [settings]="dropdownSettings"
                                               formControlName="sidControl"&gt;
                      &lt;/ng-multiselect-dropdown&gt;
  </code></pre>
  
  <p><strong>.ts file</strong></p>
  
  <pre><code>onSelectAll(selectedSIDList: Array&lt;string&gt;): void {
          selectedSIDList.forEach(sid =&gt; {
              this.selectedSIDs(sid);
              this.onItemSelect(sid);
          });
      }
  
      onItemDeSelect(deselectedSID: any): void {
          this.selectedSIDList = this.selectedSIDList.filter(s =&gt; s != deselectedSID);
  
          this.selectedSIDList.forEach(sid =&gt; {
              this.onItemSelect(sid);
          });
      }
  
      onDeSelectAll(items: any){
          console.log(items); // items is an empty array
      }
  </code></pre>