Restored the condition to execute write_uploader

resolve #2608

lib/carrierwave/mount.rb

@@ -174,8 +174,12 @@ module CarrierWave
           return if frozen?
           mounter = _mounter(:#{column})
 
-          mounter.clear! if mounter.remove?
-          write_uploader(mounter.serialization_column, mounter.identifiers.first)
+          if mounter.remove?
+            mounter.clear!
+            write_uploader(mounter.serialization_column, nil)
+          elsif mounter.identifiers.first
+            write_uploader(mounter.serialization_column, mounter.identifiers.first)
+          end
         end
 
         def #{column}_identifier
@@ -349,8 +353,12 @@ module CarrierWave
           return if frozen?
           mounter = _mounter(:#{column})
 
-          mounter.clear! if mounter.remove?
-          write_uploader(mounter.serialization_column, mounter.identifiers.presence)
+          if mounter.remove?
+            mounter.clear!
+            write_uploader(mounter.serialization_column, nil)
+          elsif mounter.identifiers.any?
+            write_uploader(mounter.serialization_column, mounter.identifiers)
+          end
         end
 
         def #{column}_identifiers

spec/orm/activerecord_spec.rb

@@ -429,6 +429,14 @@ describe CarrierWave::ActiveRecord do
         expect(@event.image_changed?).to be_truthy
         expect(@event.changed_for_autosave?).to be_truthy
       end
+
+      it "should not update image when save with select" do
+        @event.image = stub_file('test.jpeg')
+        @event.save!
+        Event.select(:id).first.save!
+        @event.reload
+        expect(@event.image).to be_present
+      end
     end
 
     describe "image?" do
@@ -1264,6 +1272,14 @@ describe CarrierWave::ActiveRecord do
         expect(@event.images_changed?).to be_truthy
         expect(@event.changed_for_autosave?).to be_truthy
       end
+
+      it "should not update image when save with select" do
+        @event.images = [stub_file('test.jpeg')]
+        @event.save!
+        Event.select(:id).first.save!
+        @event.reload
+        expect(@event.images).to be_present
+      end
     end
 
     describe "remove_images!" do