code: def visit_NameConstant(self, node):
      
      constant_val = {
          True: 'True',
          False: 'False',
          None: 'None',
      }[node.value]
      new_node = gast.Name(id=constant_val,ctx=gast.Load(),annotation=None)
      return self.visit_Name(new_node)
docs: Tangent of e.g.
      x = None
  
      Lines of this type are sometimes auto-generated by reverse-mode,
      and thus handling them is important for higher-order autodiff
      We will shunt NameConstant tangents off to visit_Name, to prevent
      code duplication.