title: Ionic 3/Angular 4 simple form validation - jit_nodeValue15(...) is not a function
body: <p>I have a super simple form, where i want to check if the user filled out the datefrom.</p>
  
  <p>Here's my form:</p>
  
  <pre><code>&lt;ion-content padding&gt;
  &lt;form #signoff="ngForm" novalidate&gt;
  &lt;ion-row&gt;
    &lt;ion-col&gt;
  
      &lt;ion-row&gt;
        &lt;ion-col class="col-left"&gt;
          &lt;label class="select_label"&gt;{{datefrom_data.title}}&lt;/label&gt;
        &lt;/ion-col&gt;
        &lt;ion-col class="col-right"&gt;
          &lt;input class="select_control" name="signoff.datefrom_name" type="date" [(ngModel)]="datefrom" (click)="showDatePicker()" required&gt;    
        &lt;/ion-col&gt;
      &lt;/ion-row&gt;
  
    &lt;/ion-col&gt;  
  &lt;/ion-row&gt;
  &lt;ion-row class="Bemerkung"&gt;
    &lt;ion-col&gt;   
      &lt;ion-label&gt;Bemerkung:&lt;/ion-label&gt;
        &lt;ion-textarea class="signoff-textarea" name="signoff.comment_name" [(ngModel)]="addtionalInfo"&gt;
        &lt;/ion-textarea&gt;
    &lt;/ion-col&gt;  
  &lt;/ion-row&gt;
  &lt;button ion-button class="maincolor" block [disabled]="!signoff.form.valid" (click)="signoff()"&gt;Kind abmelden&lt;/button&gt;
  &lt;/form&gt;
  &lt;/ion-content&gt;
  </code></pre>
  
  <p>in my signoff.ts i have the signoff() function.
  The validation on the button works but as soon as I click the button I receive a runtime error: "jit_nodeValue15(...) is not a function"</p>
  
  <p><a href="https://i.stack.imgur.com/aVjSJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/aVjSJ.png" alt="enter image description here"></a></p>
  
  <p>If I remove the form the button click event works again.</p>
  
  <p>My enviroment:</p>
  
  <p>Ionic Framework: 3.0.1
  Angular Core: 4.0.0
  Ionic App Scripts: 1.3.0</p>
  
  <p>signoff.ts:
  <a href="https://gist.github.com/anonymous/5680ad02f00d9fe40466e0b2d2409834" rel="nofollow noreferrer">https://gist.github.com/anonymous/5680ad02f00d9fe40466e0b2d2409834</a></p>
  
  <p>EDIT:
  - added signoff.ts
  - added error image</p>