AssertionError when connect to mysql and query element of a varchar-type json column

Steps:
1.Install drill 1.8.0 to the mysql server.
2.copy mysql-jdbc-connector jar to jars/3rdparty.
3.start embedded drill : bin/drill-embedded.
4.configure a mysql storage on the web console.
5.I use a sql as below:
select tb1.json_record.name from tb1 limit 100;
note:json_record is a column defined as "varchar",and there's a element called name in the json_record data structure.
then I got a error:
Error: SYSTEM ERROR: AssertionError: VARCHAR

[Error Id: a75b1588-150f-4fce-bd79-db63b9be468d on iZ25hwmeccrZ:31010] (state=,code=0)