lower empty backends/chain priority to -10.  Ref
@@ -21,9 +21,11 @@ class ChainerBackend(backend.KeyringBackend):
@classmethod
def priority(cls):
"""
- High-priority if there are backends to chain, otherwise 0.
+ If there are backends to chain, high priority
+ Otherwise very low priority since our operation when empty
+ is the same as null.
"""
- return 10 * (len(cls.backends) > 1)
+ return 10 if len(cls.backends) > 1 else -10
@properties.ClassProperty
@classmethod
