Fix `tmerge` for (partially) const types with undef fields#43812

Merged

aviatesk merged 3 commits intomasterfrom mh/fix-43784

Jan 19, 2022

Commits on Jan 14, 2022

Fix tmerge for (partially) const types with undef fields
martinholters
committed
Use === in a comparison to Union{}

martinholters
and
simeonschaub
authored

Commits on Jan 15, 2022

Fix test for #43784

martinholters
and
aviatesk
authored