S2589: Improve message in the case of null propagating operator

[costin-zaharia-sonarsource]

Description

In some cases, the problem is hard to understand and we should make this more visible for the users.

Repro steps

_componentPage = (_component?.Type == null) ? _parentComponent?.Name : _component?.Name;

or

if (_component?.Type != null)
  return $"components/{_component?.Link}";

Expected behavior

For the given examples, the message should make it clear that the null propagating operator is redundant.

Actual behavior

The raised message is "Change this expression which always evaluates to the same result." highlighting the identifier, not the operator, which can be confusing.

[rjgotten]

null coalescence operator

The ?. operator is called the null propagating operator.
The null coalescencing operator is ??

[costin-zaharia-sonarsource]

Oh yes, thanks. It seems I was with my mind in another place :)