avoid direct use of arel constants

activerecord/lib/active_record/relation/spawn_methods.rb

@@ -22,8 +22,10 @@ def merge(r)
       merged_wheres = @where_values
 
       r.where_values.each do |w|
-        if w.is_a?(Arel::Predicates::Equality)
-          merged_wheres = merged_wheres.reject {|p| p.is_a?(Arel::Predicates::Equality) && p.operand1.name == w.operand1.name }
+        if w.respond_to?(:operator) && w.operator == :==
+          merged_wheres = merged_wheres.reject { |p|
+            p.respond_to?(:operator) && p.operator == :== && p.operand1.name == w.operand1.name
+          }
         end
 
         merged_wheres += [w]