title: Error: Cannot change `multiple` mode of select after initialization
body: <p>Error image:</p>
  
  <p><a href="https://i.stack.imgur.com/mqFYI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/mqFYI.png" alt="Error image"></a>   </p>
  
  <pre><code> &lt;div fxFlex.gt-lg="100" fxFlex="100" *ngIf="requestAction == 'add'"&gt;
                      &lt;div class="pb-1"&gt;
                              &lt;md2-select placeholder="{{'WidgetType'|translate:lang}}" class="input_custom_width"(change)="widgetNode($event.value)"  required&gt;
                                  &lt;md2-option *ngFor="let widgetType of widgetTypeAry" [value]="widgetType.value"&gt;
                                      {{widgetType.name}}
                                  &lt;/md2-option&gt;
                              &lt;/md2-select&gt;
                      &lt;/div&gt;
                  &lt;/div&gt;
                &lt;div fxFlex.gt-lg="100" fxFlex="100" *ngIf="fieldsObj['node'] &amp;&amp; showRequestAction" &gt;
                  &lt;div class="pb-1"&gt;
                      &lt;md2-select placeholder="{{'Node'|translate:lang}}" [formControl]="editWidgetForm.controls['nodeId']" [(ngModel)]="nodeId" class="input_custom_width" [(multiple)]="isMultiNode" (change)="nodeChange($event.value)" required&gt;
                          &lt;md2-select-header&gt;
                              &lt;md-input-container class="input_custom_width"&gt;
                                  &lt;input mdInput type="text" placeholder="{{'Search'| translate:lang}}" [ngModelOptions]="{standalone: true}" [(ngModel)]="searchNode"/&gt;
                              &lt;/md-input-container&gt;
                          &lt;/md2-select-header&gt;
                          &lt;md2-option *ngFor="let node of nodesAry | filterPipe : searchNode" [value]="node.value"&gt;
                              {{ node.name }}
                          &lt;/md2-option&gt;
                      &lt;/md2-select&gt;
                      &lt;small *ngIf="editWidgetForm.controls['nodeId'].hasError('required') &amp;&amp; editWidgetForm.controls['nodeId'].touched" class="mat-text-warn"&gt;{{'nodeReq'|translate:lang}}&lt;/small&gt;
                  &lt;/div&gt;
                &lt;/div&gt;
  </code></pre>
  
  <p>When I use multiple in select dropdown it works fine but when I use [multiple] it only works in my edit form but not in add form .and it gives above error-Error: Cannot change <code>multiple</code> mode of select after initialization.help me to sort out this.</p>