Operators are a bit confusing in NUnit. Personally I don't fully understand how they work.

I've seen multiple times that constraint Is.Not.Null.Or.Empty is used to validate that string is not empty, which is wrong - it should be either Is.Not.Null.And.Not.Empty, or Is.Not.Null & Is.Not.Empty, or !Is.Null.Or.Empty.
But it might be missed because Not operator precedence is not obvious (one of the reasons I prefer using &/| operators instead of .And/.Or).

Since Is.Not.Null.Or.Empty constraint makes no sense (empty string or collection is always not null), I suggest always marking it as warning.

Any ideas for other commonly misused constraints?