title: Angular ng-select : selectedItems.map is not a function
body: <p>When I'm using ng-select in reactive form angular I get this error: </p>
  
  <blockquote>
    <p><strong>ERROR TypeError: selectedItems.map is not a function</strong></p>
  </blockquote>
  
  <p>I have 3 select the first two work very well but in this third one I get the error ! to map item i'm using the function (the ng-select is inside *ngFor) :</p>
  
  <pre><code>//for mappinig item : 
  mapLabelValueBS(objet) {
  return objet.map(data =&gt; {
   return {
     id: data,
     text: data.name
   }
  })
  }
  //this is the one that is causing the problem
  &lt;ng-select 
    [allowClear]="true"                                                 
    [items]="mapLabelValueBS(filieres)"
    placeholder="Filière non sélectionné"                                             
    (selected)="selecteFiliere($event)"                                                     
    formControlName="filiere"&gt;
  &lt;/ng-select&gt;
  </code></pre>
  
  <p>the result in my page (when I click on the field it doubles itself) :</p>
  
  <p><a href="https://i.stack.imgur.com/DFG9h.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/DFG9h.png" alt="enter image description here"></a></p>