Index on nullable string field?

[AxelBrinck]

Hi! I have a question about what could be the best way to deal with nullable strings.

options.Schema.For().UniqueIndex(
UniqueIndexType.Computed,
x => x.NormalizedUsername);

Net7 is complaining about NormalizedUsername would cause a possible null reference.
Because the type is "string? NormalizedUsername".

But this sould not be a problem, right?

What could be the best approach for this?

Thank you very much!