Code inspection: Redundant nullable annotation on base type constraint of type parameter constrained by another non-nullable base type

This inspection reports a nullable annotation on a type constraint when another constraint already requires the type parameter to be a non-nullable subtype. In that situation, the ? on the constraint is contradictory and has no effect.

Example

                #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
                    {
                    }
                }
            

Quick-fix

The quick-fix removes the redundant nullable annotation from the type constraint. Another quick-fix can instead annotate the other constraining types as nullable if that better matches the intended generic contract.

13 April 2026