Cast to timestamps on Druid time column leads to an exception

SELECT CAST(`ssb_druid_100`.`__time` AS TIMESTAMP) AS `x_time`,
. . . . . . . . . . . . . . . .>   SUM(`ssb_druid_100`.`lo_revenue`) AS `sum_lo_revenue_ok`
. . . . . . . . . . . . . . . .> FROM `druid_ssb`.`ssb_druid_100` `ssb_druid_100`
. . . . . . . . . . . . . . . .> GROUP BY CAST(`ssb_druid_100`.`__time` AS TIMESTAMP);

 
Error: java.io.IOException: java.lang.NumberFormatException: For input string: "1991-12-31 19:00:00" (state=,code=0)