title: How to get the angular form validation error message?
body: <p>My source code can be access by the following URL:</p>
  
  <p><a href="https://stackblitz.com/edit/angular-aidmpq?file=src%2Fapp%2Fapp.component.html" rel="nofollow noreferrer">https://stackblitz.com/edit/angular-aidmpq?file=src%2Fapp%2Fapp.component.html</a></p>
  
  <p>I want to ask the following coding:</p>
  
  <pre><code>&lt;mat-error *ngIf="logRecipients.errors.required"&gt;
      Appreciation Log Recipients is &lt;strong&gt;required&lt;/strong&gt;
    &lt;/mat-error&gt;
    &lt;mat-error *ngIf="logRecipients.errors.logRecipientValidator"&gt;
      Invalid email address
    &lt;/mat-error&gt;
  </code></pre>
  
  <p>Why the "logRecipients.errors.required" report the following error?</p>
  
  <pre><code>Cannot read property 'required' of null
  </code></pre>
  
  <p>Why the "logRecipients.errors.logRecipientValidator" prompt the following error?</p>
  
  <pre><code>Cannot read property 'logRecipientValidator' of null
  </code></pre>
  
  <p>I want to get the built-in "required" validator result to decide whether the "Appreciation Log Recipients is <strong>required</strong>" message is shown.</p>
  
  <p>I want to get my custom validator result to decide whether the "Invalid email address" message is shown. In case, the validation failed, my validator would return an object {email:true}, how can I read this attribute?</p>