title: FormControl boolean without default value in angular 2
body: <p>I'm using reactive forms in angular 2 (4.1.2)</p>
  
  <p>I have a boolean property which I don't want to have a default value but it should be required. </p>
  
  <p>This is how I create my form:</p>
  
  <pre><code>constructor(private fb: FormBuilder) {
      this.form = this.fb.group({
          payedOvertime: [false, Validators.required],
      });
  }
  </code></pre>
  
  <p>And my html:</p>
  
  <pre><code>&lt;div class="form-group"&gt;
      &lt;label&gt;Payed overtime&lt;/label&gt;
      &lt;label&gt;
          &lt;input type="radio" name="payedOvertime" formControlName="payedOvertime" [value]="true" /&gt;Yes
      &lt;/label&gt;
      &lt;label&gt;
          &lt;input type="radio" name="payedOvertime" formControlName="payedOvertime" [value]="false" /&gt;No
      &lt;/label&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>The problem is that while this works the radiobutton is preselected but I do not want that, rather it should have to be selected by clicking at one of the radio-buttons. If neither of the radiobuttons are clicked I want the form to be invalid.</p>