add error for invalid species in search

app/models/item.rb

@@ -58,7 +58,9 @@ class Item < ActiveRecord::Base
       items = Table(:objects)
       if @property == 'species'
         species = Species.find_by_name(self)
-        # TODO: add a many-to-many table to handle this relationship
+        raise ArgumentError, "Species \"#{self.humanize}\" does not exist" unless species
+        # TODO: add a many-to-many table to handle this relationship, if
+        # performance becomes an issue
         ids = items[:species_support_ids]
         condition = ids.eq('').or(ids.matches_any(
           species.id,

spec/models/item_spec.rb

@@ -168,5 +168,9 @@ describe Item do
     specify "should not be able to search other attributes thru filters" do
       lambda { Item.search('id:1').all }.should raise_error(ArgumentError)
     end
+    
+    specify "should raise exception if species not found" do
+      lambda { Item.search('species:hurfdurfdurf').all }.should raise_error(ArgumentError)
+    end
   end
 end