Box Search API with only NOT operators always return Bad request

Hi box team,
As the last time I use Box Search API (few months ago) my query is valid and it returns the correct value I need. But now when I run my system again (Not change for source code) it always return error due to bad request.
Here is the image of the request I use by POST MAN.

Note that when a change the query from <NOT "ABC"> to <NOT "ABC" AND NOT "ABC"> It works. It is very lucky for me that I could find out a solution in this time. My team had to release product to my customer. 

So I hope you can fix this problem.

Thank you