title: EXTJS 6 Modern: buffered store + grid: Uncaught TypeError: Cannot read property 'length' of undefined
body: <p>Here is the fiddle
  <a href="https://fiddle.sencha.com/?fiddle=1ahm#fiddle/1ahm" rel="nofollow">https://fiddle.sencha.com/?fiddle=1ahm#fiddle/1ahm</a></p>
  
  <p>Classic theme with nearly the same code works fine.</p>