where not null in C#

C# offers a 'where T : notnull' generic constraint that ensures type parameters cannot be null, working with both reference types and non-nullable value types. This constraint provides a safer alternative to 'where T : class' or 'where T : struct' by preventing null values while allowing flexibility in type usage. It's particularly useful for creating null-safe APIs for dictionary keys, IDs, and value objects without forcing specific type categories.