I get what you are saying.  I tend to declare them as `NULL` as it indicates the fact that they haven't been initialized at all.  That way, in cases that they cannot be initialized the values can be set to `FALSE` which would indicate an attempt to have been set, providing some distinction.

Initializing to `NULL` lets the variables fail `isset` - which seems accurate until they are set - without the `NOTICES` that come along with simply not declaring the property.