title: H2O GLM function not recognizing data passed in as H2OFrame
body: <p>I don't understand why I'm getting the error below. I've imported csv data as an h2oFrame. It's clearly an h2oFrame since I can perform methods such as describe() and such. But, when I pass it in to the glm function, I'm getting the rror saying that it's not the proper datatype. Why is this occurring? </p>
  
  <pre><code>dat = h2o.import_files(data_dir)
  glm_normal = H2OGeneralizedLinearEstimator(family='gaussian') 
  glm_normal.train(x=x, y=y, train_frame=dat) 
  </code></pre>
  
  <p><strong>Error:</strong> 
  H2OTypeError: Argument <code>training_frame</code> should be an H2OFrame, got NoneType None</p>