title: Warning: Contour not rendered for constant ZData
body: <p>Anyone can help me solve this error?</p>
  
  <blockquote>
    <p>Warning: Contour not rendered for constant ZData<br>
    In contourf>parseargs at 467<br>
    In contourf at 64<br>
    In example at 298 </p>
  </blockquote>
  
  <p>Thanks in advance</p>