While upgrading to GraphQL Java 21, I stumbled over the method valueToLiteral offered by the Coercing interface. So far, when implementing a custom scalar, I haven't bothered about implementing this method and have not encountered any problems so far although the default implementation throws an exception.

In the JavaDoc of the Coercing interface, it says that "every valid external input values for parseValue(Object) is also valid for valueToLiteral(Object) and vice versa" which suggest that the argument to valueToLiteral should be in serialized form. However, when looking at implementations of this method, I see that most often serialze is called first on the argument, which suggests otherwise.

Could you please improve the JavaDoc and also the documentation on custom scalars, which does not mention this method at all?