[Basic UI] Frames generate errors with null items

[reyhard]

Which UI are you reporting an issue for?

• Basic UI
• HABPanel
• HABot
• CometVisu

The problem

After upgrading from 4.0m2 to 4.0m4 I've noticed that Sitemap frames are producing following error when sitemap is rendered in either PC web browser or Android phone.

[ui.internal.items.ItemUIRegistryImpl] - Failed to retrieve item during widget rendering, item does not exist: Item 'null' could not be found in the item registry

Adding some random existing item to frame seems to "solve" this issue

Frame label="label" item=SomeRandomItemThatExist {

Expected behavior

No errors in the events.log

Steps to reproduce

Create sitemap with frames and then try to view it on i.e. phone.

Following sitemap should generate 3 error lines mentioned above

sitemap alarmclock label="Alarms" {
    Frame label="1" item=Thermostat_Automatic_Program  {
        Switch item=AlarmClock_Switch icon="screen" 
    }
    Frame label="2" {
        Text item=Phone_01_AlarmClockDate label="Alarm 1 [%s]" icon="time"
    }
    Frame label="3" {
        Text item=Phone_02_AlarmClockDate label="Alarm 2 [%s]" icon="time"
    }
}

[lolodomo]

It is probably a regression introduced last Sunday by either openhab/openhab-core#3644 or openhab/openhab-core#3635.
I will have a look.

[lolodomo]

Log level was changed from DEBUG to WARN in openhab/openhab-core#3644.
This change has to be reverted.

[lolodomo]

Closed by openhab/openhab-core#3686