title: Cloud function exception in Flutter
body: <p>I'm facing an issue after updating all my libraries to comply with AndroidX.
  Specifically, when I try to use the package "cloud_functions", I receive this error message:</p>
  
  <pre><code>flutter: throwing generic exception
  flutter: Exception: Unable to call function funName
  </code></pre>
  
  <p>Now, I didn't touch the code handling the call, I simply updated the packages in the yaml file.</p>
  
  <p>My code is:</p>
  
  <pre><code>cfResponse = await CloudFunctions.instance.call(
        functionName: 'funName',
        parameters: {
          "p1": p1,
          "p2": p2,
        },
      ).then((response) {
        return response;
      }).catchError((error) {
        print(error);
        return null;
      });
  </code></pre>
  
  <p>I'm having the same issue both on Android and iOS.</p>
  
  <p>My libraries are at version:<br>
  - cloud_functions: ^0.1.1<br>
  - firebase_auth: ^0.8.1+4</p>
  
  <p>I'm on Flutter 1.2.1 and Dart 2.1.2</p>