def source(self, unit=None):
    cls = self.__class__
    plug = self._mplug.source()
    node = Node(plug.node())
    if (not plug.isNull):
        return cls(node, plug, unit)
def source(self, unit=None):
    cls = self.__class__
    plug = self._mplug.source()
    node = Node(plug.node())
    if (not plug.isNull):
        return cls(node, plug, unit)