title: Angular 5 - async pipe with firebase
body: <p>I want to add async pipe to angular firebase but i've got error that I don't know how to fix:</p>
  
  <blockquote>
    <p>ERROR Error: InvalidPipeArgument: '[object Object]' for pipe
    'AsyncPipe'</p>
  </blockquote>
  
  <p>Firebase NoSQL database:</p>
  
  <pre><code>{
    "boss" : [ null, {
      "isPremium" : true,
      "name" : "John",
      "students" : 10000
    } ],
    "users" : [ null, "user", "user2" ]
  }
  </code></pre>
  
  <p><strong>UPDATE</strong></p>
  
  <p><strong>I've changed component code:</strong></p>
  
  <pre><code>user$: AngularFireList&lt;any&gt;;
  
    constructor(db: AngularFireDatabase) {
      this.user$ = db.list("/users");
    }
  </code></pre>
  
  <p>html:</p>
  
  <pre><code>&lt;ul&gt;
    &lt;li *ngFor="let user of user$ | async"&gt;
      {{ user }}
    &lt;/li&gt;
  &lt;/ul&gt;
  </code></pre>
  
  <p>I'm getting the same error... 
  In Angular version 4 it works but, how to fix that in angular 5.2.0 ??</p>