If-Then statement not properly displaying duration (G18) of two dates (E18 & F18)

E18 - Start Date (5/7/18)
F18 - End Date (5/10/19)
G18 - Duration in days (# days)

G18 has the following formula:
=IF(AND(DATEDIF(E19,F19,"yd")=0),"1",DATEDIF(E19,F19,"yd"))&IF(DATEDIF(E19,F19,"yd")=1," day"," days")

I dragged G18 down to apply the formula to the rows below it (ie. G19, G20, G21, etc.), however E19/F19, E20/F20, E21/F21, etc. don't have any dates in them yet, so I want to keep G19, G20, G21, etc. blank.

Currently, G19, G20, G21, etc. have "1 day" in them, which I don't want. It should be blank, but with the formula running for when dates are entered in E and F. Any suggestions? Thanks!