class_docstr: Adds Return statement when they are implicit,
  and adds the None return value when not set
  
  >>> import gast as ast
  >>> from pythran import passmanager, backend
  >>> node = ast.parse("def foo(y): print(y)")
  >>> pm = passmanager.PassManager("test")
  >>> _, node = pm.apply(NormalizeReturn, node)
  >>> print(pm.dump(backend.Python, node))
  def foo(y):
      print(y)
      return builtins.None
code: def __init__(self):
      super(NormalizeReturn, self).__init__(CFG)
  
imports: from pythran.analyses import CFG, YieldPoints
  from pythran.passmanager import Transformation
  import gast
label_desc: Use image node_id 1 to create a new NormalizeReturn object from inherited base classes: Transformation with example: obj = NormalizeReturn()