presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/storage/StorageType.java/StorageType/mapOf
class StorageType:    public static StorageType mapOf(StorageType keyStorageType, StorageType valueStorageType)
    {
        return new StorageType(format("%s<%s,%s>", MAP_TYPE_NAME, keyStorageType.getHiveTypeName(), valueStorageType.getHiveTypeName()));
    }