'Removes the topmost item from the stack, will return the
old value or `None` if the stack was already empty.'

def pop(self):

    stack = getattr(self._local, 'stack', None)
    if (stack is None):
        return None
    elif (len(stack) == 1):
        release_local(self._local)
        return stack[(-1)]
    else:
        return stack.pop()
