Make sure the prefix is a class (ROOT-5856).
Make sure the prefix is a class (ROOT-5856).

karies/cling,root-mirror/cling,karies/cling,karies/cling,marsupial/cling,perovic/cling,marsupial/cling,root-mirror/cling,karies/cling,root-mirror/cling,marsupial/cling,perovic/cling,marsupial/cling,marsupial/cling,karies/cling,perovic/cling,marsupial/cling,root-mirror/cling,perovic/cling,root-mirror/cling,karies/cling,root-mirror/cling,perovic/cling