bugfixes (#3078)

* fix phpdoc
* fix invoice export field order
* prevent empty migration warning
* do not trigger export validation on new timesheets
* update license year
* remove trailing comma in function call for php compatibility
* add new composer plugin config
* bump phpunit schema version

src/Validator/Constraints/TimesheetExportedValidator.php

@@ -38,6 +38,10 @@ final class TimesheetExportedValidator extends ConstraintValidator
             throw new UnexpectedTypeException($timesheet, TimesheetEntity::class);
         }
 
+        if ($timesheet->getId() === null) {
+            return;
+        }
+
         if (!$timesheet->isExported()) {
             return;
         }