Do not display result when cell is empty (date)

Hello,

How to leave a blank result when the cell of the formula is empty?

Here's my explanation:
I want to get the date J+1 (excluding weekends) and leave the cell blank when no date is provided.

My file looks like this:
Column F => day J
Column G => J+1 excluding weekends

So the formula is: IF(WEEKDAY(F3)=6, F3+3, F3+1)

For example: when F2=10/09/2014 then G2=11/09/2014
when F3=12/09/2014 then G3=15/09/2014 (because the 12th is a Friday and I’m looking for the next working day)

So far so good :)

My problem is that when column F is not filled, a result still shows in the cells of column G: 01/01/1900

I know that the formula/condition to avoid this would be something like: IF(ISBLANK(F3), """,
but I can’t seem to merge those two formulas.... -_-'

I tried: =IF(ISBLANK(F3), """, (WEEKDAY(F3)=6), F3+3, F3+1)
but apparently there is an error that I can’t identify

Can you help me?
I’m using Excel 2003
Thank you