Code inspection: Redundant nullable annotation on base type constraint of type parameter having non-nullable type kind

This inspection reports a nullable annotation on a type constraint when another constraint such as class, struct, unmanaged, or notnull already makes the type parameter non-nullable. In that case, the ? on the constraint is contradictory and has no effect.

                #nullable enable
                using System;
                class C
                {
                    void M<T>() where T : notnull, IDisposable?
                    {
                    }
                }
            

                #nullable enable
                using System;
                class C
                {
                    void M<T>() where T : notnull, IDisposable
                    {
                    }
                }
            

Depending on the constraint list, another quick-fix can remove the redundant non-nullable type-kind constraint instead.

13 April 2026