Duplicate field name: %s

Raise code

            if name not in self.fields:
                self.fields[name] = field
                continue
            if (
                    not isinstance(field, Struct) or
                    not isinstance(self.fields[name], Struct)
            ):
                raise ValueError('Duplicate field name: %s' % name)
            self.fields[name] = self.fields[name] + field
        for id, (_, field) in enumerate(viewitems(self.fields)):
            field._set_parent(self, id)
        super(Struct, self).__init__(viewvalues(self.fields))
        self._frozen = True

    def _struct_from_nested_name(self, nested_name, field):