in src/JetBrains.Space.Generator/CodeGeneration/CSharp/Extensions/ApiFieldExtensions.cs [137:153]
public static bool RequiresAddedNullability(this ApiField subject)
{
// For certain optional types, add nullability if not present
// Note this logic is different from the Kotlin SDK generator,
// to make sure the resulting code is C#-friendly.
return subject.Optional &&
subject.DefaultValue == null &&
!subject.Type.Nullable && (
(subject.Type is ApiFieldType.Primitive primitiveType && (
primitiveType.ToCSharpPrimitiveType() == CSharpType.String ||
primitiveType.ToCSharpPrimitiveType() == CSharpType.Bool))
||
subject.Type is ApiFieldType.Enum
);
}