## The problem

POSTing to /api/v1/evaluate with a null context value, e.g. {"flag_key":"profile","entity_id":"...","context":{"cohort":null}}, returns HTTP 400 with {"code":3,"message":"proto: (line 1:102): invalid value for string type: null"}. This was a breaking change in v1.5.0 that was not in the changelog.

## What fixed it

Fixed in Flipt v1.5.1, upgrade and null context values are accepted again. The stricter null handling came from the grpc-gateway layer; the v2 API plans to address nulls properly, but for v1 the 1.5.1 patch restored the previous behavior.