Fix role icon & emoji assignment.

[csmir]

Closes #2376

Cause for actions:

If the Icon/Emoji args are specified as null, the Optional still thinks it has an underlying value (being null) There was a check for this in place, which made null values empty Optional, but this means they're never sent to the API because they never populate the json. To fix this, I am forcing a default populated value on the emoji if set as null: "". This is sent as an empty value to the API, and removed internally.