exchange: allow passing no includes/excludes to `pull()`
I would expect that `exchange.pull(includepats=[])` results in an empty list of
include patterns to be passed to the remote, but it doesn't currently because we
check for any truthy value instead of checking specifically for `not None`.
# name space package to host third party extensions
import pkgutil
__path__ = pkgutil.extend_path(__path__, __name__)