Designing for Nullability in C#

With Nullable Reference Types (NRTs) enabled by default in .NET 6 templates, designing APIs that clearly communicate nullability is no longer optional—it’s expected.

Enabling NRTs

<PropertyGroup>
    <Nullable>enable</Nullable>
</PropertyGroup>

Guard Clauses

Use the new .NET 6 helper to throw if null.

public void SetName(string name)
{
    ArgumentNullException.ThrowIfNull(name);
    _name = name;
}

Key Takeaways

• Use `string?` to explicitly mark nullable strings.
• Use `!` (null-forgiving operator) sparingly—only when you truly know better than the compiler.
• Enable `Nullable` to enforce discipline.