Fix S2955 FP: Comparing nullable type with null

[paulhickman-ec]

Description

The following code causes S2955. However comparing to default(T) instead of null as the rule suggests gives a compiler error. Even if it did compile, if T was int then default(T) would be zero which gives different behavior than comparing T? to null.

Repro steps

public bool Foo<T>(Func<T?> bar) where T : notnull
{
    T? t = bar();
    return t == null;
}

Expected behavior

Rule does not fire

Actual behavior

Rule does fire

Known workarounds

Ignore the rule

Related information

• SonarAnalyzer.CSharp 9.28.0.94264
• .Net 8

[zsolt-kolbay-sonarsource]

Thank you for reporting the issue. Confirmed as False Positive.