Merge pull request #2139 from mcmire/issue_2078_master

Fix for #2078 (against master)

activerecord/lib/active_record/relation/finder_methods.rb

@@ -243,7 +243,7 @@ def apply_join_dependency(relation, join_dependency)
     end
 
     def construct_limited_ids_condition(relation)
-      orders = relation.order_values
+      orders = relation.order_values.map(&:presence).compact
       values = @klass.connection.distinct("#{@klass.connection.quote_table_name table_name}.#{primary_key}", orders)
 
       relation = relation.dup

activerecord/test/cases/associations/eager_test.rb

@@ -1048,4 +1048,16 @@ def test_joins_with_includes_should_preload_via_joins
       assert_not_equal 0, post.comments.to_a.count
     end
   end
+
+  def test_join_eager_with_empty_order_should_generate_valid_sql
+    assert_nothing_raised(ActiveRecord::StatementInvalid) do
+      Post.includes(:comments).order("").where(:comments => {:body => "Thank you for the welcome"}).first
+    end
+  end
+
+  def test_join_eager_with_nil_order_should_generate_valid_sql
+    assert_nothing_raised(ActiveRecord::StatementInvalid) do
+      Post.includes(:comments).order(nil).where(:comments => {:body => "Thank you for the welcome"}).first
+    end
+  end
 end