I have the cell return wrong value

ie. M cell returns #VALUE!
where M cell forumla is =SUM(I2*AU2)
I2= 20871

and
AU2 cell is no value pluged in"
where AU2
=IF(ISERROR((AM2/(AG2+AJ2+AM2)*AD2)*A2*1.05/840/AL2), "",ROUND((AM2/(AG2+AJ2+AM2)*AD2)*A2*1.05/840/AL2,3))


Now, I do not want the M cell returns with #VALUE!, i want it blank or if the
future there is a value in AU2, it returns a correct number.

thanks
gar
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