Warlock resources bar problem

[Rainrider]

Here is my try at the warlock resources bar: https://gist.github.com/Rainrider/5246884

However, when testing this on a toon that does not have the prereq spells, I get the following error:

oUF: Error: Style [Rain] attempted to register event [SPELLS_CHANGED] on unit [player] with a handler that doesn't exist.

I checked Phanx' code as a reference and it seems to me (s)he does the same thing: registers the handler for the event from within the handler, but does not have any errors.

Could someone explain the difference I fail to see please?