Use .to_s on _reflections lookup

activerecord/lib/active_record/associations.rb

@@ -1612,7 +1612,7 @@ def destroy_associations
         has_many name, scope, hm_options, &extension
 
         reflection = ActiveRecord::Reflection::AssociationReflection.new(:has_and_belongs_to_many, name, scope, options, self)
-        self.reflections = self.reflections.except(middle_reflection.name).merge!(name => reflection)
+        self.reflections = self.reflections.except(middle_reflection.name).merge!(name.to_s => reflection)
       end
     end
   end

activerecord/lib/active_record/reflection.rb

@@ -85,7 +85,7 @@ def reflect_on_association(association)
 
       #   @api private
       def _reflect_on_association(association) #:nodoc:
-        _reflections[association]
+        _reflections[association.to_s]
       end
 
       # Returns an array of AssociationReflection objects for all associations which have <tt>:autosave</tt> enabled.