title: [TypeError: undefined is not an object (evaluating 'headers.Authorization = "Bearer " + userToken')]
body: <p>I have a generic Api for my app, I am setting headers.authorization to Bearer+token but its not working. I checked by consoling userToken it displays fine there, but can not really update headers with it...  need a little push here :)</p>
  <pre><code>export default async (url, method, token, body) =&gt; {
   let headers;
    if (token) {
      const userToken = await AsyncStorage.getItem('token');
      headers.Authorization = `Bearer ${userToken}`;
    }
  
    const structure = {
      url,
      method,
      headers,
    };
  </code></pre>