I have the following formula that i need some advice on.

=(SUM(F5/'[Workbook1.xlsx]Sheet1'!$H$4)*'[Workbook1.xlsx]Sheet1'!$H$5+G5)
The formula works fine if there is a value in F5 but if its blank, i get a #value! in D5.
I am not that familiar with IF functions and i have tried on my own but cant seem to get it to work to show blank if the referenced cell is blank.
Any assistance would be great!!

thanks