Conditional format when value equals Zero

[Anonymous]

Hello, I have a particular problem when I use conditional format to make a Heat-map. There are values equal to 0 that I want to be painted red, but there are other that theorithically have no value at all, that are blank, and I need the color for those to be white.

The logic of the count function is:
#Executed activities / #Total Activities

In some cases there are no activities at all (blank values), in that case how can I paint them white?