private String extractName(ImmutableSchema search) {
        return search != null ? search.getName() : globalRankProfilesKey;
    }
Mapping from name to {@link RankProfile} as well as a reverse mapping of {@link RankProfile} to {@link Schema}.
Having both of these mappings consolidated here make it easier to remove dependencies on these mappings at
run time, since it is essentially only used when building rank profile config at deployment time.

Global rank profiles are represented by the Search key null.

@author Ulf Lilleengen
config-model/src/main/java/com/yahoo/schema/RankProfileRegistry.java