500 error when character's species or rarity is removed

[SpeedyD]

Bug as reported:

Description of bug: When a character has their rarity or species removed, the masterlist entry will give out a 500 error. (As well as other parts of the site that rely on having a visible rarity or species for characters.)
This is due to the fact that both rarity and species have displayNames that require there to actually be rarity and species attached.
How was the bug caused (exact steps to reproduce): Remove the species or rarity of a character. This happens.

Further details

Frankly, the issue isn't that a 500 error appears after this happens; the issue is that it SHOULD NOT BE POSSIBLE to remove species or rarity. This is already blocked in character creation and design updates, as far as I'm aware, but somehow not in the trait editing modal.