Make userform open when a blank cell in a range is selected, and not open if value in it

I have a userform that I need to have open when a blank cell in Range ("A8:A51") is selected, but I don't need the userform to appear if the cell selected in Range("A8:A51") already has a value or text in it.

The code I have now works but when I select any other cell on the sheet outside my range I get a Run-time error "91' Object variable or With block variable not set.

Here is my code:

Please Login or Register  to view this content.

I have tried a couple different scenarios but can't seem to figure it out. Any advice??

Thanks