[BLUEJ-1308] Kubuntu 20.04: BlueJ doesn't open editor

After updating my system from Kubuntiu 19.10 to 20.04 Bluej doesn't open the editor any longer:

Start BlueJ

Create new project

Create new class

Right click on class, selection of "Open Editor" -> nothing happens

Reinstalling BlueJ 4.2.2. doesn't change anything.

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