class_docstr: A type that allows no values.
  
  Used to represent expressions
  that are undefined, either because they do not exist mathematically
  or because the code to generate the expression has not been
  implemented yet.
  
  Parameters
  ----------
  why_null : str
      A string explaining why this variable can't take on any values.
code: def filter_variable(self, other, allow_convert=True):
      raise ValueError("No values may be assigned to a NullType")
  
file_path: Theano/theano/gof/null_type.py
imports: from __future__ import absolute_import, print_function, division
  from theano.gof.type import Type
label_desc: Use image node_id 3 for calling the NullType obj's underlying member method code with example usage: obj.filter_variable(other, allow_convert) without return types