def fetch(key, default=nil)
      found_in = self_and_sub_collections.detect{ |c| c[key] }
      raise KeyError unless found_in
      found_in[key]
    end
def fetch(key, default=nil)
      found_in = self_and_sub_collections.detect{ |c| c[key] }
      raise KeyError unless found_in
      found_in[key]
    end
Public: Returns a check or collection if it's in the check collection

 key - a check or collection name
 throws a KeyError when the key is not found