Test at the wikimania. It has now been resolved.

@Sjoerddebruin , Yes I agree with you. I also thought about it when rewriting the gadget, but there wasn't much documentation on it and I'm not kept informed since.

@Ricordisamoa : Yes, maybe, I didn't know that but, it's a warning which appear on first loading data via the API. So its just to handle any possibilities of answer. Secondly, the warning shouldn't appear, because of those lines at the begining :

var itemId = mw.config.get( 'wbEntityId' );
	if ( !itemId ) {
		return;
	}

Was also on many aliases creation. The issue is now resolved.

@Mbch331 : I know, I'm not very good at spelling, even in French XD. I will explain my thought.