text: /* @flow */
  
  const base64 = require('base-64');
  
  let asBase64: string;
  asBase64 = base64.encode('some string');
  
  let asString: string;
  asString = base64.decode('c29tZSBzdHJpbmc=');
  
  // $FlowExpectedError
  asString = base64.decode(null);
  