Usually, including in “hypermedia”, but “hypermedia” is either an adjective or a mass noun, not a countable noun of which you can have a single instance.
“a hypermedia... ” looks like you are using it as an adjective to modify a countable noun, and when there is no noun looks like you forgot the noun; “JSON is not a hypermedia unto itself...” should probably be something “JSON isn’t hypermedia unto itself... ” (I’d actually prefer “JSON, on its own, isn’t hypermedia”, but that gets behind the issue with the use of the indefinite article.
We take english grammar from the corrupt! The rich! The oppressors of generations who have kept you down with myths of uncountable nouns... and we give it back to you... the people.
