Apache Flink

Trying to understand the correct way to have my UDF process a value and the time column with this example:
```203     sliding_window = Slide.over(lit(4).hours).every(lit(20).minutes).on(col("event_time")).alias("w")
204 
205     mean_table = input_table.window(sliding_window) \
206                         .group_by(col("device_id"), col('w')) \
207                         .select(col("device_id"), vector_mean(col('sensor_mm'), col('w')), col('w').rowtime.alias("end_time"))```
When I pass in the time column I get SQL errors like the following:
&gt;  py4j.protocol.Py4JJavaError: An error occurred while calling o8.executeSql.
&gt; : java.lang.RuntimeException: Not support visitor: org.apache.flink.table.planner.plan.utils.ExpandTableScanShuttle$ExpandTableScanInSubQueryShuttle@6d09d4a4
I"m not sure what the exception is trying to tell me, but I'd like to process this window with the value and the time.

Also it seems if I do this into my UDF call, things seem to work as expected:
```vector_mean(col('sensor_mm'), col('end_time'))```
Which I'm not sure is entirely what i want