User Field Formula when some values aren't assigned

I have a User Field formula which references two other UF values. For some of the tasks, the UFV is not assigned.
For example, my formula is
UFV("CY")+ UFV("SF") 
In once case it could be 1+1 =2
2nd case it could be " " + 1 = This is returning blank
I want it to be " " + 1 = 1

Use a formula like the following:
UFV_ZERO("User Field Name) + UFV_ZERO("User Field Name 2")
UFV("User Field Name") returns UNSET if there is no assigned value causing the whole calculation to be blank
UFV_ZERO("User Field Name") returns empty string if no assigned value, resulting in the desired outcome of " " + 1 = 1