Unexpected ConsistentHashPercentageBucketer behavior

[jakekaplan]

If ConsistentHashPercentageBucketer has a key_whitelist, calling flag.is_enabled() without providing the key as the condition will always result in a consistent score of 0.32 from hashing an empty dictionary. I would expect this to feature to always be enabled instead of it being based on the % given to the bucket.

Example:

from flipper.bucketing import ConsistentHashPercentageBucketer
from flipper import FeatureFlagClient, MemoryFeatureFlagStore
from flipper.bucketing.percentage import Percentage
features = FeatureFlagClient(MemoryFeatureFlagStore())

MY_FEATURE = 'MY_FEATURE'
features.create(MY_FEATURE)
features.enable(MY_FEATURE)

features.set_bucketer(MY_FEATURE, ConsistentHashPercentageBucketer(key_whitelist=["user_id"], percentage=Percentage(0.5)))
features.is_enabled(MY_FEATURE)
>>> True

features.set_bucketer(MY_FEATURE, ConsistentHashPercentageBucketer(key_whitelist=["user_id"], percentage=Percentage(0.31)))
features.is_enabled(MY_FEATURE)
>>> False


item = features._store.get(MY_FEATURE)
item._meta.bucketer._serialize_checks({})
>>> b'[]'
serialized = item._meta.bucketer._serialize_checks({})
hashed = hashlib.sha1(serialized)
score = item._meta.bucketer._score_hash(hashed)
score
>>> 0.32