code: public static <T> Collection<T> emptyCollection(MultiMapConfig.ValueCollectionType collectionType) {
          switch (collectionType) {
              case SET:
                  return Collections.emptySet();
              case LIST:
                  return Collections.emptyList();
              default:
                  throw new IllegalArgumentException("[" + collectionType + "] is not a known MultiMapConfig.ValueCollectionType!");
          }
      }
docs: Picks right empty collection type, like {@link java.util.Collections#emptySet()}
  or {@link java.util.Collections#emptyList()} )} depending on the
  {@link com.hazelcast.config.MultiMapConfig#valueCollectionType}
  
  @param collectionType one of {@link MultiMapConfig.ValueCollectionType#SET}
  or {@link MultiMapConfig.ValueCollectionType#LIST}
  @return empty collection like {@link java.util.Collections#emptySet()}
  depending on the collectionType argument
  @throws java.lang.IllegalArgumentException if collectionType is unknown