SQL Developer line chart report not working

Hi

I'm not sure if I'm in the right group for my question:

I'd like to create a user defined report in SQL Developer 19.1. Database version ist 12.1. (But actually I tried also with SQL Developer 19.4 without success).

My query is:

SELECT b.wait_class wait_class

   , TO_CHAR(TRUNC(a.end_time,'MI'),'HH24:MI') end_time

   , ROUND((SUM(a.time_waited) / 10),2) sample_count

 FROM gv$waitclassmetric_history a

 JOIN gv$system_wait_class b

  ON a.wait_class# = b.wait_class#

  AND a.inst_id = b.inst_id

 WHERE b.wait_class = 'System I/O' 

 GROUP BY TRUNC(a.end_time,'MI')