class_docstr: Base class for missing values in supervised learning.
class_docstr_tok: ["Base","class","for","missing","values","in","supervised","learning","."]
docstr: Helper function
  Replace a column in the sframe with Nones
  Type of the original column is preserved
docstr_tok: ["Helper","function","Replace","a","column","in","the","sframe","with","Nones","Type","of","the","original","column","is","preserved"]
code: def fill_with_na(self, sf, colname):
      """
      Helper function
      Replace a column in the sframe with Nones
      Type of the original column is preserved
      """
      ret = sf.copy()
      if colname in sf.column_names():
          ret[colname] = tc.SArray([None] * len(sf), sf[colname].dtype)
      return ret
  
imports: from __future__ import print_function
  from __future__ import division
  from __future__ import absolute_import
  import unittest
  import turicreate
  import array
  from turicreate.toolkits._main import ToolkitError
label_desc: Use image node_id 2 for calling the SupervisedLearningMissingValueTest obj's underlying member method code with example usage: obj.fill_with_na(sf, colname) and returns: ret