Tezos_raw_protocol_alpha.Destination_storageval must_exist :
Raw_context.t ->
Destination_repr.t ->
Raw_context.t Tezos_protocol_environment_alpha.Error_monad.tzresult
Tezos_protocol_environment_alpha.Lwt.tmust_exist ctxt dest checks whether the given destination dest exists in the context ctxt. If the destination exists, a new context is returned with gas consumed for the lookup cost. If it does not exist, an error is returned.