title: com.facebook.react.bridge.readablenativemap cannot be cast to java.lang.string
body: <p>My code:</p>
  <pre><code>const file = {
    uri: this.state.imageSource,
    name: this.state.imageName,
    type: 'image/jpg',
  };
  
  const data = new FormData();
  data.append('file', file);
  
  fetch(config.server + '/upload', {
    method: 'POST',
    body: data,
  })
    .then((res) =&gt; res.json())
    .then((responseData) =&gt; {
      alert(JSON.stringify(responseData));
    })
    .catch((err) =&gt; {
      alert(err);
    });
  </code></pre>
  <p>Without <strong>FormData</strong> code doesnt display error. What I should do to fix? Debugging on android.</p>