Not possible to set weight of board scope to None or 0

Steps to reproduce

• open issue board
• click edit board
• select none or 0 as weight

What is the current bug behavior?

selected weight is not persisted, any weight is shown instead:

Screen_Recording_2019-05-07_at_21.37.49

What is the expected correct behavior?

• issues with no weight set are shown for none
• issues with weight set to 0 are shown for 0

Blocked by: #12588 (closed)