Postgres column doesn't roundtrip for type `Maybe (Vector Text)`

[roberth]

I have a table with

    labels :: Columnar f (Maybe (Vector Text))

Inserts work fine. Nothing and Just [] are distinct in the database, as expected.
However, queries return Just [] when they should Nothing.

This might be a problem with the FromBackendRow instance for Maybe and/or Vector.

Found on beam version 6b3e4c9

[LaurentRDC]

The issue is because of this line:

beam/beam-postgres/Database/Beam/Postgres/Types.hs

Line 162 in 15af356

Just SqlNull -> pure mempty

There is a special switch when parsing Vector, but in this instance, we should never expect a null. Pull request incoming

[LaurentRDC]

The fix for this issue was released in beam-postgres 0.5.4.2