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 visit_Return(self, node):
      if not node.value and not self.yield_points:
          none = ast.Attribute(
              ast.Name("builtins", ast.Load(), None, None),
              "None",
              ast.Load(),
          )
          node.value = none
          self.update = True
      return node
  
file_path: pythran/pythran/transformations/normalize_return.py
imports: from pythran.analyses import CFG, YieldPoints
  from pythran.passmanager import Transformation
  import gast
label_desc: Use image node_id 3 for calling the NormalizeReturn obj's underlying member method code with example usage: obj.visit_Return(node) and returns: node