bug地址： https://issues.apache.org/jira/browse/FLINK-31375?filter=-2
bug详细内容：
the values of map<string,string> are truncated by the CASE WHEN function.
// sql
create table test (a map<varchar, string>) with ('connector'='print');
insert into test select * from (values(case when true then
map['test','123456789'] else map ['msg_code','0', 'msg_reason', 'abc'] end));
the result:
+I[{test=123}]
We hope the value of result is '123456789', but I get '123', the length is
limited by 'abc'.
