kazoo.recipe.watchers.ChildrenWatch calls _func() with a Boolean value

[diranged]

I'm still trying to track down how we go Kazoo to do this (it seems like its related to some kind of connection failure) -- but in Kazoo 2.0+ we're seeing occasional exceptions thrown in our nd_service_registry code when the watcher calls self._func(children) and the passed in children seems to be a bool.

Stack Trace:

Traceback (most recent call last):
  File "/mnt/.venv/lib/python2.7/site-packages/kazoo/recipe/watchers.py", line 333, in _get_children
    result = self._func(children)
  File "/mnt//.venv/lib/python2.7/site-packages/nd_service_registry/watcher.py", line 197, in _update_children
    self._children = sorted(children)
TypeError: 'bool' object is not iterable

Relevant nd_service_Registry code:
https://github.com/Nextdoor/ndserviceregistry/blob/v1.0.0/nd_service_registry/watcher.py#L197

def _update_children(self, children):
        """Function executed by Kazoo upon children changes for a path.

        This function is registered by the _update() method during and is
        executed by Kazoo upon any children changes to a path. Its responsible
        for updating the local list of children for the path, and executing
        the appropriate callbacks.

        args:
            children: The list of children returned by Kazoo
        """
        self._children = sorted(children)
        log.debug('[%s] Children change detected: %s' %
                  (self._path, self._children))
        self._execute_callbacks()

I'm looking at a short-term fix where I just return with a warning if children isn't the list we expect.. but still pretty strange. This seems to happen in conjunction with issue #254.