test: doctest for addNullEmbedFilters #1815

Job	Run time
Test (Nix)	7m 31s
Get FreeBSD build from CirrusCI	5m 15s
Build MacOS (Nix)	13m 59s
Build Linux static (Nix)	6m 30s
Build Linux (Stack)	2m 54s
Build MacOS (Stack)	4m 57s
Build Windows (Stack)	4m 48s
Lint & check code style	1m 47s
Test memory (Nix)	5m 6s
Test PG 9.6 (Nix)	6m 10s
Test PG 10 (Nix)	5m 43s
Test PG 11 (Nix)	5m 58s
Test PG 12 (Nix)	7m 35s
Test PG 13 (Nix)	5m 52s
Test PG 14 (Nix)	6m 22s
Test PG 15 (Nix)	5m 56s
Build Linux (Cabal, GHC 9.0.2)	26m 50s
Build Linux (Cabal, GHC 9.2.4)	21m 29s
Build aarch64 (Cabal, GHC ${{ matrix.ghc }})	0s
Prepare release	0s
Release on GitHub	0s
Release on Docker Hub	0s
Release Arm Builds on Docker Hub	0s
Remove copied files from server	0s
	2h 24m 42s

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