Excel IF blocks in combination with sheet referencing

Im trying to get an re ordered set of columns from a spreadsheet, to do this with out touching the original data ive been using =Sheet1!U71 in column A and then dragging it down to take in U72,U73,U74 etc

This is all fine, but when there are blanks its keeps throwing a 0 into the cell.

Ive been trying to use an if block as below =IF(ISBLANK(Sheet1!U71), ,=Sheet1!U71)

But cant seem to get it to work, is it possible to do this with an if block whilst referencing another sheet, or is it an issue with my IF syntax ?