title: How to display first letter of name instead of image in matListAvatar?
body: <p>I have a mat list like below</p>
  
  <pre><code>&lt;mat-list&gt;
    &lt;mat-list-item *ngFor="let person of Persons"&gt;
      &lt;img matListAvatar src="../../../assets/images/person.svg" [alt]="person.firstName"&gt;
      &lt;h3 matLine&gt; {{Person.name }} &lt;/h3&gt;
      &lt;mat-divider&gt;&lt;/mat-divider&gt;
    &lt;/mat-list-item&gt;
  &lt;/mat-list&gt;
  </code></pre>
  
  <p>I want to replace the avatar with first letter of first name of person if avatar is not found. How can I do that? Any help is appreciated?</p>