now.getDayOfMonth() fails in rule

Setup, Configuration and Use Scripts & Rules
1

Hello,
I would like to display the current day of the month in a rule. Unfortunately the script fails at this point:

rule "Zaehlerstaende while test"
when
	 Time cron "0 0/1 * * * ?"
	
then

var heute = now.getDayOfMonth() // 11 (11.09.2022)
logError("heute", heute)

end

Error in Log: 2023-01-08 10:55:00.850 [ERROR] [internal.handler.ScriptActionHandler] - Script execution of rule with UID ‘benachrichtigungen-3’ failed: An error occurred during the script execution: Could not invoke method: org.openhab.core.model.script.actions.Log.logError(java.lang.String,java.lang.String,java.lang.Object[]) on instance: null in benachrichtigungen

I’m totally clueless because I use this method in a few other rules with no problem. I am very grateful for help!

Openhabian: openHAB 3.3.0

Thanks!
André