Not all dialog made empty when deleting data layer

[DTeelde@…]

What steps will reproduce the problem?

1. Download some data from OSM
2. Open the dialog voor Tags and Relations
3. Select an node or way with tags; the tags will be shown in the dialog
4. Delete the data layer

What is the expected result?

The lists within the dialogs should be cleared

What happens instead?

The tags of the previous node/way are kept in the list. Also the downloaded relations still exists in the list of Relations.

Choosing the drown down menu item 'Download (incomplete) members' or a relation will cause such an error.

Please provide any additional information below. Attach a screenshot if possible.

=== STACK TRACE ===
Thread: AWT-EventQueue-0 (19) of main
java.lang.NullPointerException
	at java.util.Objects.requireNonNull(Unknown Source)
	at org.openstreetmap.josm.gui.dialogs.relation.DownloadRelationMemberTask.<init>(DownloadRelationMemberTask.java:73)
	at org.openstreetmap.josm.actions.relation.DownloadSelectedIncompleteMembersAction.actionPerformed(DownloadSelectedIncompleteMembersAction.java:57)
	at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
	at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
	at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
	at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
	at javax.swing.AbstractButton.doClick(Unknown Source)
	at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
	at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(Unknown Source)
	at java.awt.AWTEventMulticaster.mouseReleased(Unknown Source)
	at java.awt.Component.processMouseEvent(Unknown Source)
	at javax.swing.JComponent.processMouseEvent(Unknown Source)
	at java.awt.Component.processEvent(Unknown Source)
	at java.awt.Container.processEvent(Unknown Source)
	at java.awt.Component.dispatchEventImpl(Unknown Source)
	at java.awt.Container.dispatchEventImpl(Unknown Source)
	at java.awt.Component.dispatchEvent(Unknown Source)
	at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
	at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
	at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
	at java.awt.Container.dispatchEventImpl(Unknown Source)
	at java.awt.Window.dispatchEventImpl(Unknown Source)
	at java.awt.Component.dispatchEvent(Unknown Source)
	at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
	at java.awt.EventQueue.access$500(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
	at java.awt.EventQueue$4.run(Unknown Source)
	at java.awt.EventQueue$4.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
	at java.awt.EventQueue.dispatchEvent(Unknown Source)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.run(Unknown Source)

[DTeelde@…]

Print screen of the situation

[Don-vip]

Regression somewhere between r13878 (works fine) and r13996 (does not work).

EDIT: regression of r13925 + r13926: r13924 works. r13926 does not.

[Don-vip]

In 14156/josm:

fix #16615 - make sure dataset can be garbage collected after removal (regression from r13926)

[Don-vip]

@Florian: if you make this test with Mapillary plugin installed you will notice the field org.openstreetmap.josm.plugins.mapillary.gui.imageinfo.AddTagToPrimitiveAction#target retain the value of the selected OSM primitive, thus forbidding the garbage collector to free memory for the entire dataset. Can you please fix it?