title: x.y Activity is not a concrete class error message in manifest
body: <p><a href="https://i.stack.imgur.com/u88fh.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/u88fh.png" alt="enter image description here"></a></p>
  
  <p>I got ... <strong>"is not a concrete class"</strong> error in manifest file. </p>
  
  <p>The app works though. I can build and test without problem but this error bugs my eyes. Please help if you can.</p>
  
  <p>When <strong>I ctrl + click on the activity name on the manifest it even opens the .java src file.</strong></p>
  
  <p>(The activity is actually called "MapInputActivty" - typo i know, but this is not the problem.)</p>