Wait, is this line required here?

Yeah, it complains about conversion without !:

Argument of type 'Expression<Func<TEntity, object>>' cannot be used for parameter 'propertiesExpression' of type 'Expression<Func<TEntity, object?>>' in 'IProperty[] UpsertCommandBuilder.ProcessPropertiesExpression(IEntityType entityType, Expression<Func<TEntity, object?>> propertiesExpression, bool match)' due to differences in the nullability of reference types.

I thought about making _matchExpression object? as well, but probably it shouldn't ever point to nullable property.

It might be worth validating that through tests, as the expression might be inflated on in memory EF

Could you clarify what to validate exactly?

I thought about adding integration test with nullable Exclude property, but currently Nullable=false for integration tests project.

Hmm.. good point - in which case it's probably safe to just merge it :D

I'll probably run a test (or check if we have one that won't have issues excluding columns that have null values). It shouldn't, but I want to try sanity check just to cover all bases

I thought about making _matchExpression object? as well, but probably it shouldn't ever point to nullable property.

Ah, I assume you mean this sentence. It's not that it wouldn't work or fail if matchExpression leads to nullable property - ProcessPropertiesExpression doesn't care if it's nullable or not, it simply inspects expression, that's it.

It's just semantically matchExpression leads to PK or unique index, so the column shouldn't be nullable.