Updating to a new Reference Type Value throws error

Issue Summary

Updating to a new reference type value in the attribute page for an already create Object Reference attribute throws an error on save.

Steps to Reproduce

1. Create an Object with an Object Reference Attribute.
2. Click into the additional value column and change it.
3. Click Update. (Nothing happens).
4. Click Update again. (Error is thrown)

Expected Results

The additional value should change

Actual Results

Nothing happens after first update and the second update throws an error

Workaround

 The new reference type value is created so after clicking out and clicking back in, you will be able to change the reference type value to the new value.

Affected Version 

 8.7.7