use `decodeUtf8'` in JSONB's PersistField instance

[Vlix]

first (badParse $ TE.decodeUtf8 bs) $ eitherDecodeStrict bs

could probably be

import Data.Either (fromRight)
...
first (badParse (fromRight "<Invalid UTF-8>" $ TE.decodeUtf8' bs)) $ eitherDecodeStrict bs