It would make me happy if the message could be changed, and maybe ERRCODE_INVALID_PARAMETER_VALUE also changed, perhaps to one of the JSON-specific ones in the 2203x range.
I'd agree with this.
By the same token, the message and the errcode are established current behavior, so there can be sound arguments against changing them (even though that means weird logic in rewriting the expression).
This is not a technology issue, I'd be pretty willing to see what some
more experienced people say about this. I think just documenting the