DateTime conversion to string does not work as expected [SOLVED]

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    • Hardware: CPUArchitecture/RAM/storage
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    • Java Runtime Environment: which java platform is used and what version
    • openHAB version: 2.5.11
  • Issue of the topic: please be detailed explaining your issue
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Hello I have a problem which I could not solve so far
Ich have a item with format datetime but which does not have a value all the time

.items File

DateTime           PZ_overlay_expiry        "Overlay Expiry"        { channel="tado:zone:a5022236:2:overlayExpiry" }

The target ist to store the value in a virtual item (to be displayed in happanel or paperui)

virtual.item File

String  PZ_habpanel_expiry "[%s]"

As the value of the item ist not a real value all the time


2021-01-09 10:08:37.394 [vent.ItemStateChangedEvent] - PZ_overlay_expiry changed from NULL to UNDEF
2021-01-09 18:33:15.763 [vent.ItemStateChangedEvent] - PZ_overlay_expiry changed from UNDEF to 2021-01-09T18:33:04.000+0000
2021-01-09 19:11:53.060 [vent.ItemStateChangedEvent] - PZ_overlay_expiry changed from 2021-01-09T18:46:10.000+0000 to UNDEF

I added some if condition and tried various rules, but I could not succeed


rule "Temp_Patrickzimmer_Umbau"
       Item PZ_overlay_expiry changed 
      if (PZ_overlay_expiry.state != NULL || PZ_overlay_expiry.state != UNDEF) {
      PZ_habpanel_expiry.postUpdate(String::format("%1$tH:%1$tM", PZ_overlay_expiry.state))}

// I also tried in the then condition:

  if  ...{
      var String tmp = PZ_overlay_expiry.state.format("%1$tH:%1$tM")

But I get errors

2021-01-09 20:13:35.778 [ERROR] [ntime.internal.engine.RuleEngineImpl] - Rule 'Temp_Patrickzimmer_Umbau': H != org.eclipse.smarthome.core.library.types.DateTimeType

Error of second variant

2021-01-09 20:12:05.562 [ERROR] [ntime.internal.engine.RuleEngineImpl] - Rule 'Temp_Waschkueche_Umbau': H != java.lang.String

what is wrong ?

Could solve it with help of REST


if (PZ_overlay_expiry.state != NULL && PZ_overlay_expiry.state != UNDEF) {
      else PZ_habpanel_expiry.postUpdate("")