dev/core#2019 - Changing a case custom field from blank to something doesn't show properly what changed

[demeritcowboy]

Overview

https://lab.civicrm.org/dev/core/-/issues/2019

1. Create a custom field for cases.
2. Create a case and leave the custom field blank.
3. Change the custom field to something, let's say "Orange".
4. Look in the resulting Change Custom Data activity on the case. It says it changed from "Orange => Orange", whereas you'd expect it to indicate the previous value was blank.

Before

Incorrect record of what changed.

After

Correct.

Technical Details

api customvalue.getdisplayvalue does an empty() check on the passed in value and then considers that to mean it should use the existing field value in the database instead, but it's already been updated and so contains the new value, so this then incorrectly treats '' and 0 which are legitimate prior values.

This api function doesn't appear to be used anywhere in universe, and was added in 5.19 for this function, so changing it is unlikely to affect anyone.

Comments

Has test.

This also includes a belated test for #19692 since the only thing extra needed to test that is to also run this test here in another locale, which it does.

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[demeritcowboy]

Thanks!