note 17265 deleted from migration4.empty by philip

Note Submitter: alan at frostick dot de ---- The changes to empty() also affect isset() in a similar way. Under php3: $foo=""; isset($foo) returned false.. but under php4 it returns true, because the variable is defined. I discovered this when converting other people's code to php4. They used isset() unnecessarily - with the implicit expectation it just tested the value of the variable as being non-null. Although I don't agree with sloppy coding, it can give an unexpected shock when run under php4 and so any uses of isset() should be searched for before you attempt to migrate.