A variable without a value is displayed in the “Variable log” as deleted

[rusiaikinat]

Environment

Version: 2.0.999-SNAPSHOT

Bug Description

The variable creation form (Process instance → Runtime → Variables → Create) allows saving a variable with a non-Null type without providing a value. Value should be required for any type other than Null.

As a downstream effect, such a variable (non-Null type, empty value) is then displayed in the variable history (History → Variable log) with change type Delete, since that is how the history view interprets an empty value on a non-Null-typed variable.

Steps To Reproduce

1. Open a running process instance → Runtime tab → Variables.
2. Click "Create", select a type other than Null (e.g. Date), leave the value empty, and click "Save".
3. Go to History → Variable log.

Current Behavior

• The variable is saved successfully with no value, even though its type is not Null.
• In History → Variable log, this variable appears with change type Delete.

bandicam.2026-09-16.11-44-48-540.mp4

Expected behavior

• The value field should be required when the variable type is not Null; saving without a value should not be allowed.
• As a result, a variable should never end up in the "non-Null type + empty value" state, and should not be misrepresented as Delete in the variable history.

[NikitaShchienko]

QA Notes

Fix: a Date process variable created with the untouched default value was saved as null (shown as deleted in the Variable log).

• Open an active process instance → Runtime → Variables → Create.
• Enter a name, select type Date (value is pre-filled with the current date/time).
• Click Save without touching the value.
• Expected: the variable is created with the pre-filled date (seconds :00); Variable log shows a create entry, not a deletion.