title: Firebase callable function not receiving arguments
body: <p>Implementing a simple function on typescript to call a Firebase callable function is not working.
  Using firebase-tools@4.0.3 -g, firebase-functions@2.0.5, firebase@5.3.1</p>
  
  <p>Firebase callable function:</p>
  
  <pre><code>import * as functions from "firebase-functions";
  
  exports.httpsOnCall = functions.https.onCall((data, context) =&gt; {
    console.log(data);
    return data;
  });
  </code></pre>
  
  <p>It is deployed correctly</p>
  
  <p>Calling the function in webapp:</p>
  
  <pre><code>const a = Firebase.functions.httpsCallable("httpsOnCall");
    a.call({ a: 1, b: "testing", c: true }).then(result =&gt; {
      console.log(result);
    });
  </code></pre>
  
  <p>Firebase object initialization:</p>
  
  <pre><code>import * as firebase from "firebase";
  
  const config = {
    apiKey: "asdasdasd",
    authDomain: "APPNAME.firebaseapp.com",
    databaseURL: "https://APPNAME.firebaseio.com",
    projectId: "APPNAME",
    storageBucket: "APPNAME.appspot.com",
    messagingSenderId: "123456"
  };
  firebase.initializeApp(config);
  const Firebase = {
     functions: firebase.functions()
  }
  </code></pre>
  
  <p>Log from firebase:</p>
  
  <pre><code>null
  </code></pre>
  
  <p>Log from webapp:</p>
  
  <pre><code>{data: null}
  </code></pre>
  
  <p>It seems like data is not reaching the httpsOnCall function, even though the context variable is populated.</p>