How to put the model class as a multi_search args?

my action is like this
weblogs=Weblog.multi_search(query,[Weblog,Reg])
but i kept getting this:
You have a nil object when you didn’t expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.map

in class_method.rb -id_multi_search

anyone who could show me an answer?
thx…