Avoid crash when no defaults

Author: untitaker

vdirsyncer/cli/utils.py

@@ -468,7 +468,8 @@ def format_storage_config(cls, header=True):
     from ..utils import get_class_init_specs
     handled = set()
     for spec in get_class_init_specs(cls, stop_at=Storage):
-        defaults = dict(zip(spec.args[-len(spec.defaults):], spec.defaults))
+        defaults = spec.defaults or ()
+        defaults = dict(zip(spec.args[-len(defaults):], defaults))
         for key in spec.args[1:]:
             if key in handled:
                 continue