Cannot Revise Contract when Buyer field is made required

Symptom

You cannot revise a contract when Buyer field is made required in Application Designer.
You may experience issues where you cannot revise a contract record when some fields are made required via Application Designer.

To Replicate:

1- Open Maximo as maxadmin
2- Go to Application Designer, search for Purchase Contract app
3- Edit the main tab in that app and change input mode on buyer field to required (control properties)
4- Save record
5- Go to Purchase Contracts and create a new contract
6- Fill required fields, including Buyer field and save contract record
7- Approve the contract
8- Select Action > Revise Contract
9- Enter new description and click OK. As a result Maximo allows you to revise it.
10- Now, make sure you have an approved contract where the buyer field is blank.
11- Go to the approved contract where the buyer field is blank and try to Revise it

The error below shows:
System Message
BMXAA4195E - A value is required for the Buyer field.

And on 2nd attempt, the same error shows up and you'll get additional error message:

System Message
BMXAA4129E - The record for Contract=KC2276, Revision=1, Organization=KEY2 already exists. This validation error is thrown when an attempt is made to insert a new record with a unique key value
that already exists in the database. Ensure that the key value for the given record is unique.

This happens when you want to revise a contract that had a Buyer field null in some
of the previous revisions.