title: set error " errors : {__zone_symbol__state: null, __zone_symbol__value: Array(0)}" by Angular 4 validator
body: <p>Mobile mobileNumberValidator returns fine but the other two validators returns a null promise on errors. Cant identify the mistake i have done here. Please help.
  Those two validators sets errors in formbuilder object as follows</p>
  
  <p>errors
  :
  {__zone_symbol__state: null, __zone_symbol__value: Array(0)}</p>
  
  <p>In form builder group</p>
  
  <pre><code> this.empInfoForm = this.fb.group({
        'Mobile': [null, [Validators.required], [this.mobileNumberValidator.bind(this)]],
        'Private': [null,  [this.privateNumberValidator.bind(this)]],
        'Work': [null, [this.workNumberValidator.bind(this)]],  
      });
  </code></pre>
  
  <p>Validator Methods</p>
  
  <pre><code>  mobileNumberValidator(control: AbstractControl) {
  
          return new Promise(resolve =&gt; {
            setTimeout(() =&gt; {
              if (!this.isMobileNumberValid) {
                resolve({
                  'phoneNumber': true
  
                })
              console.log(this.empInfoForm)
              } else {
                resolve(null);
              }
            }, 10);
          })
        }
          workNumberValidator(control: AbstractControl) {
  
          return new Promise(resolve =&gt; {
            setTimeout(() =&gt; {
              if (!this.isWorkNumberValid) {
                resolve({
                  'phoneNumber': true
  
                })
                 console.log(this.empInfoForm)
              } else {
                resolve(null);
              }
            }, 10);
          })
        }
          privateNumberValidator(control: AbstractControl) {
  
          return new Promise(resolve =&gt; {
            setTimeout(() =&gt; {
              if (!this.isPrivateNumberValid) {
                resolve({
                  'phoneNumber': true
  
                })
  
                    console.log(this.empInfoForm)
              } else {
                resolve(null);
              }
            }, 10);
          })
        }
  </code></pre>