godot-module-template/engine/modules/mono/editor/Godot.NET.Sdk/Godot.SourceGenerators/CodeAnalysisAttributes.cs

namespace System.Diagnostics.CodeAnalysis
{
    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue)]
    public sealed class NotNullAttribute : Attribute
    {
    }
}