Swing UI elements not initialized

Hello,
in my plugin I'm using some forms (f.e. for Language settings) created by Intellij

RMB -> New -> Swing UI Designer -> Create Dialog Class

But that generated component in some cases fails that elements are null -> it seems that when developing a plugin (running gradle runIde) all is ok, but once released and installed from marketplace it fails:

java.awt.IllegalComponentStateException: contentPane cannot be set to null.
	at java.desktop/javax.swing.JRootPane.setContentPane(JRootPane.java:594)
	at java.desktop/javax.swing.JDialog.setContentPane(JDialog.java:1036)
	at gdscript.settings.GdDownloadSdk.<init>(GdDownloadSdk.java:24)
	at gdscript.settings.component.GdSettingsComponents.addSdk$lambda$3(GdSettingsComponents.kt:65)
	at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1972)
	at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2313)
	at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405)
	at java.desktop/javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:262)
	at java.desktop/javax.swing.AbstractButton.doClick(AbstractButton.java:374)
	at java.desktop/javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:1028)
	at java.desktop/javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:1072)
	at java.desktop/java.awt.Component.processMouseEvent(Component.java:6656)
	at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3385)
	at java.desktop/java.awt.Component.processEvent(Component.java:6421)
        ...

How are those components supposed to be initialized?