title: Function has a return type of 'Future<String>' but doesn't end with a return statement
body: <p>I am writing a Future method in Dart (flutter). It simply runs a query on Firebase and returns the result. But even before writing my business logic, I am getting a warning message says:</p>
  
  <blockquote>
    <p>[dart] This function has a return type of 'Future', but
    doesn't end with a return statement. [missing_return]</p>
  </blockquote>
  
  <p>Below is my Future function:</p>
  
  <pre><code>Future&lt;String&gt; getLikeCount(documentID) async {
      Firestore.instance.collection('favorites').where(documentID).getDocuments().then((data){
        return 'test';
      });  
    }
  </code></pre>
  
  <p>I get the basic idea of why the error is happening, I assume that because there is a 'then' inside, till it happens the function returns nothing. How to overcome this issue?</p>