class_docstr: A custom action to convert empty strings passed by shell to None in
  python. This is necessary as shell scripts print null strings when a
  variable is not specified. We could use the more apt None in python. 
class_docstr_tok: ["A","custom","action","to","convert","empty","strings","passed","by","shell","to","None","in","python",".","This","is","necessary","as","shell","scripts","print","null","strings","when","a","variable","is","not","specified",".","We","could","use","the","more","apt","None","in","python","."]
code: def __call__(self, parser, namespace, values, option_string=None):
      if values.strip() == "":
          setattr(namespace, self.dest, None)
      else:
          setattr(namespace, self.dest, values)
  
imports: from __future__ import print_function
  from __future__ import division
  import argparse
  import logging
  import math
  import os
  import subprocess
  import sys
  import threading
label_desc: Use image node_id 1 for calling the NullstrToNoneAction obj's underlying member method code with example usage: obj.__call__(parser, namespace, values, option_string) without return types