[getnormality]

It doesn't treat them as equal, it treats them as one group. It does this because the result is more useful.

It is not the case that nulls are always the same as one another. It is also not the case that nulls are always distinct from each other. Thus, the normal rule of grouping, that same values are combined and distinct values make different groups, does not apply. Another principle is needed to determine the result of grouping with nulls.

Logic which allows for an unknown value can't be shoehorned into always giving definite true or false answers.