CharType lost in the creation of MaxAggFunction & MinAggFunction

CharType lost in AggFunctionFactory#createMinAggFunction(Retract) and
AggFunctionFactory#createMaxAggFunction(Retract&nonRetract).
If execute

SELECT Max('a') ...

, The following exception will throw.

Caused by: org.apache.flink.table.api.TableException: Max aggregate function does not support type: ''CHAR''.
Please re-check the data type.
at org.apache.flink.table.planner.plan.utils.AggFunctionFactory.createMaxAggFunction(AggFunctionFactory.scala:395)
at org.apache.flink.table.planner.plan.utils.AggFunctionFactory.createAggFunction(AggFunctionFactory.scala:76)
at org.apache.flink.table.planner.plan.utils.AggregateUtil$.$anonfun$transformToAggregateInfoList$1(AggregateUtil.scala:444)