SQL Server Slowest Query is NULL

I am looking at both the SQL Server expensive queries report and the query below, but both are showing this mysterious NULL query as the slowest query on my server.

Is there any way I can find out more about this NULL query and why it might be so slow?

Is this some internal query? It doesn’t seem like this should be showing up in the report if so.

This is the query which is also showing NULL as the slowest query on my server:

select 
    r.session_id,
    r.status,
    r.command,
    r.cpu_time,
    r.total_elapsed_time,
    t.text
from 
    sys.dm_exec_requests as r
cross apply 
    sys.dm_exec_sql_text(r.sql_handle) as t

How can I find out what this query is and why it’s so slow?