title: How does BigQuery ML deals with NULL numeric features?
body: <p>With categorical features, we can see that BigQuery ML automatically creates a "_null_filler" dummy variable by running ML.WEIGHTS on the created model, which makes sense.</p>
  
  <p>In the case of numeric features, the missing values are imputed using the mean or something else? And are those two behaviors mentioned anywhere in the official documentation?</p>