Remove a custom background image causes black screen in greeter

Enviroment:

current build number: 204
device name: frieza
channel: ubuntu-touch/rc-proposed/bq-aquaris-pd.en
last update: 2016-10-06 08:32:15
version version: 204
version ubuntu: 20161006
version device: 20160809.0
version custom: 20160831--42-26-vivid

Reproduce:
1. Go System settings>Background>Custom
2. Take a picture and set it as your new background image(check it by locking/unlocking device)
3. Go back to System settings>Background, remove the custom background and lock device
4. Unlock it and check the greeter is black

What happens:
background turns black when removing a custom background image. If this is working as design, then a black/non background option should be listed

What did I expect:
 would be great if the default background image is set again automatically when a custom image is removed or list an option to have no background image