grails yui richEditor and the div _firebugConsole : Why it appears in my richEditor ?

Question

I use the richEdit yui component to my grails application. I added a constraints size:1..1000 on my grails domain class.

But when I save the content of the richEditor, no validation message is rendered if the richEditor is blank. The richEditor contains automatically the message :

(I use the extension firebug).

How can I avoid it ?

Thanks