title: Error trying to diff ''. Only arrays and iterables are allowed
body: <p>I keep getting the following console error:</p>
  
  <pre><code>Error trying to diff 'Paul'. Only arrays and iterables are allowed
  </code></pre>
  
  <p><strong>HTML:</strong></p>
  
  <pre><code>&lt;fieldset class="one-quarter sm-padding"&gt;
      &lt;label&gt;Occupation&lt;/label&gt;
      &lt;select name="occupations"
              [(ngModel)]="occupations" 
              (ngModelChange)="showValuePromptText('Occupation', $event)"&gt;
          &lt;option *ngFor="let occupation of occupations" 
                  [value]="occupation"&gt;
              {{occupation}}
          &lt;/option&gt;
      &lt;/select&gt;
  &lt;/fieldset&gt;
  </code></pre>
  
  <p><strong>TS:</strong></p>
  
  <pre><code>import { Component } from '@angular/core';
  import { PromptService } from '../../services/prompt.service';
  import { IPromptText } from "../../models/IPromptText";
  
  @Component({
      selector: 'fact-find',
      templateUrl: './factfind.component.html',
      styleUrls: ['./factfind.component.css'],
      providers: [PromptService]
  })
  
  export class FactFindComponent {
      promptTexts: IPromptText[];
      currentPromptText : string;
  
      showDefaultPromptText(fieldName: string) {
          if (fieldName != null) {
              this.promptService.fetchPrompts(fieldName, '').subscribe(
                  (data) =&gt; this.currentPromptText = data
              );
          }
      }
  
      showValuePromptText(fieldName: string, fieldValue: string) {
          if (fieldValue != null) {
              this.promptService.fetchPrompts(fieldName, fieldValue).subscribe(
                  (data) =&gt; this.currentPromptText = data
              );
          }
      }
  
      occupations: string[] = ["John", "Paul", "George", "Ringo"];
  }
  </code></pre>
  
  <p>If anyone could shed some light on how I can fix this it would be greatly appreciated.</p>