The default media type for cache types is APPLICATION_UNKNOWN if not explicitly configured by the user. However, APPLICATION_UNKNOWN is not supported when using the following:

• Filters
• Converters
• Transcoders (works sometimes, best effort)

Instead of failures occurring at runtime, we should throw a configuration exception where possible. In the case of the transcoder, we should either throw a more meaningful exception when transcoding fails or remove the ability to transcode APPLICATION_UNKNOWN sources.

The exception(s) should instruct the user to explicitly configure the media type.