title: How to Prevent Build Warning: " NSData may not respond to 'dataWithBase64EncodedString:' "
body: <p>The following code produces this build warning:</p>
  
  <blockquote>
    <p>NSData may not respond to
    'dataWithBase64EncodedString:'</p>
  </blockquote>
  
  <p>The code:</p>
  
  <pre><code>NSString * message = @"string string string";
  
  NSData *data= [NSData  dataWithBase64EncodedString:(NSString *)message];
  </code></pre>
  
  <p>How do I fix this to remove this warning?</p>