Apache Flink

Can i insert null values into flink table?
`insert into table1(col1) select null;`
```Exception in thread "main" org.apache.flink.table.api.ValidationException: SQL validation failed. From line 1, column 159 to line 1, column 162: Illegal use of 'NULL'
        at <http://org.apache.flink.table.planner.calcite.FlinkPlannerImpl.org|org.apache.flink.table.planner.calcite.FlinkPlannerImpl.org>$apache$flink$table$planner$calcite$FlinkPlannerImpl$$validate(FlinkPlannerImpl.scala:186)
        at org.apache.flink.table.planner.calcite.FlinkPlannerImpl.validate(FlinkPlannerImpl.scala:113)
        at org.apache.flink.table.planner.operations.SqlToOperationConverter.convert(SqlToOperationConverter.java:261)
        at org.apache.flin```