presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/systemtables/TableMetadataSystemTable.java/TableMetadataSystemTable/getStringValue
class TableMetadataSystemTable:    static String getStringValue(NullableValue value)
    {
        if ((value == null) || value.isNull()) {
            return null;
        }
        return ((Slice) value.getValue()).toStringUtf8();
    }