title: Angular custom validator not returning error code
body: <p>Hi guys I have created custom validator for my form and its working fine - detecting the error as expected but when it does detect it the errors in FormGroup object is empty but valid is properly set to false</p>
  
  <pre class="lang-js prettyprint-override"><code>export function ValidateBody(control: AbstractControl): ValidationErrors {
    if (control.value.length &lt; 3) return { tooShort: true };
    if (control.value.length &gt; 50) return { tooLong: true };
    if (/[^a-zA-Z0-9 \-\/]/.test(control.value)) return { invalidChar: true };
    return null;
  }
  </code></pre>
  
  <pre class="lang-js prettyprint-override"><code>export class FormQuestionComponent {
    @Input() question: FormData&lt;any&gt;;
    @Input() form: FormGroup;
    get isValid() {
      if (!this.form.controls[this.question.key].valid)
        console.log(this.form.errors);
      return this.form.controls[this.question.key].valid;
    }
  }
  </code></pre>
  
  <p>I have no idea why I'm getting null in the console even when form is invalid. I have also tried to make inputs validated by build in Validators valid but still no errors given.</p>