Why DeprecationReason is an empty string in introspection

I noticed that `codegen`, very popular tool to generate types from a schema, marks as `deprecated` all the possible types, queries, and mutations.
After some debugging I found out that the `deprecationReason` is returned by the introspection as an **empty string**.
For some reasons, `codegen` gives more importance to it than `isDeprecated` field (which is correctly set to `false`).
I checked around and I saw an old MR of @MarkKremer that fixed this problem.
But looking at the code now, it looks like that change has been reverted.
Any explanation for it?
I still think it makes sense to have the reason set to `nil` rather than an empty string.