Unable to remove Discord ID for an account through the Dashboard

[robere2]

Describe the bug
When you try to remove a user's Discord account, the edit will fail. This is because it is sending an empty string "" in the request instead of null.

To Reproduce
Steps to reproduce the behavior:

1. Open the dashboard page https://www.rpi.tv/dashboard/users
2. Edit or create a User and assign an 18-digit Discord ID
3. Edit that User again and empty the Discord ID box
4. Save. An error snackbar will appear at the bottom of the screen.

Expected behavior
The edit should succeed and the user no longer has a Discord account associated with their RPI TV account.