[HELP] Ambulance Job

hello, i am getting this error while being ambulance boss and trying to open workers list.
[ERROR] [MySQL] Check the error above, an error happens when executing the callback from the query : “SELECT firstname, lastname, identifier, job, job_grade FROM users WHERE job = @job ORDER BY job_grade DESC {@job=ambulance}”
Error running call reference function for resource esx_society: citizen:/scripting/lua/scheduler.lua:403: server/main.lua:192: attempt to index a nil value (field ‘?’)
stack traceback:
server/main.lua:192: in upvalue ‘ref’
citizen:/scripting/lua/scheduler.lua:389: in function citizen:/scripting/lua/scheduler.lua:388
[C]: in function ‘xpcall’
citizen:/scripting/lua/scheduler.lua:388: in function citizen:/scripting/lua/scheduler.lua:387
stack traceback:
[C]: in function ‘error’
citizen:/scripting/lua/scheduler.lua:403: in function citizen:/scripting/lua/scheduler.lua:372