presto-thrift-api/src/main/java/io/prestosql/plugin/thrift/api/datatypes/PrestoThriftVarchar.java/PrestoThriftVarchar/toBlock
class PrestoThriftVarchar:    @Override
    public Block toBlock(Type desiredType)
    {
        checkArgument(desiredType.getClass() == VarcharType.class, "type doesn't match: %s", desiredType);
        return sliceType.toBlock(desiredType);
    }