SQL Server Slowest Query is NULL
That's a system session.
DBCC INPUTBUFFER(37); might give a clue what it's doing, or CROSS APPLY with  sys.dm_exec_input_buffer(), but you might not be able to understand any more about what it's doing. Since it's a background task, it is unlikely to be a cause for any other perceived slowness but, being internal, I'm not sure what you could possibly do to tune it anyway...
If you're just randomly checking dm_exec_requests you should probably limit it to non-system sessions (join to sys.dm_exec_sessions where is_user_process = 1). Why it's not filtered out of the report, I have no no idea, I tend to not use built-in reports because I (and vendors) build much better versions.