Scoping by weight 'none' in Board scope doesn't work

Summary

Setting the Weight filter to Any, None, or 0 in a Board scope all seem to do the same thing - they set the weight filter to 'Any Weight'. This means you cannot scope issues that have no weight assigned, or only to issues with a weight of 0. This filter does seem to work if add it in the board search bar.

Steps to reproduce

1. Create an Issue with a weight of 1
2. Create an Issue Board
3. Edit board - scoping on Weight: None

What is the current bug behavior?

The Weight value in the modal will show Any Weight, and when saving the board, will display issues of all weights.

What is the expected correct behavior?

The Weight value in the modal should show Weight: None. When saving the board, only issues without a weight should appear.

Output of checks

This bug happens on GitLab.com (GitLab Enterprise Edition 11.8.1-ee)