title: Async Validator Throw Expected validator to return Promise or Observable
body: <p>I have tried to confirm the password with password value. I have done as per Async validator standard. But I am wondering it's not working and throw me the following error. Please tell anyone how to solve this error. </p>
  
  <blockquote>
    <p>Expected validator to return Promise or Observable.</p>
  </blockquote>
  
  <p>Here is my code.</p>
  
  <p>Call Validators:</p>
  
  <pre><code>cPass: ['', Validators.compose([
    Validators.required, 
    Validators.maxLength(32),
    Validators.minLength(10)
  ]),
    this.validPassword.bind(this)
  ]
  </code></pre>
  
  <p>Custom Validation funciton:</p>
  
  <pre><code>validPassword(control: AbstractControl) {            
    const isEqual = Observable.of(this.password == control.value);
    return isEqual ? { valid : true } : null;         
  }
  </code></pre>