Search Term to check if acceptedByList is empty

Is there any operator to check if the taskInfo.acceptedByList is empty (not in rules but in search term)

I am using a PCTaskHelper.searchUserTask to get tasks in user inbox. Now I want to filter the tasks not accpeted by user. I tried all possible combination in search term but nothing seems to be working. The query gives my both assigned & accepted user tasks.

e.g
fields = {"#{currentTask.taskInfo.acceptedByList}"};
operator = “is empty”
operator = “Is Empty”
operator = “isEmpty”
operator = “=” value = null

Thanks in advance.

Can you try equals (=) to empty String array, e.g. new String[] {}

Alex

Thanks Alex for quick response.

I tired this option too but it is not working. It returns zero length Task[].
I have 2 tasks in my inbox (1 not accepeted , 1 accepted)