presto-parquet/src/main/java/io/prestosql/parquet/ParquetEncoding.java/ParquetEncoding/initDictionary
class ParquetEncoding:        @Override
        public Dictionary initDictionary(ColumnDescriptor descriptor, DictionaryPage dictionaryPage)
                throws IOException
        {
            return PLAIN.initDictionary(descriptor, dictionaryPage);
        }