NPE after deleting a MatParam 2x

[stephengold]

At commit: 4cd137d
To reproduce: 6, 1, Select geometry, 1, Select parameter, 1, Delete, Z, Delete
Expected: darker model with fewer material parameters
Got:

Sep 07, 2021 9:22:55 AM jme3utilities.nifty.BasicScreenController perform
SEVERE: Caught unexpected throwable:
java.lang.NullPointerException
	at maud.model.cgm.MatParamRef.<init>(MatParamRef.java:90)
	at maud.model.cgm.SelectedMatParam.makeRef(SelectedMatParam.java:230)
	at maud.model.cgm.SelectedMatParam.delete(SelectedMatParam.java:78)
	at maud.action.DeleteAction.process(DeleteAction.java:92)

Hypothesis: cloning bug in Material or MatParam

Note that after the undo, the parameter type and value are both displayed as "null"! They should be "Vector4" and "Color[0.7058824, 0.6509804, 0.6, 1.0]" respectively.

[stephengold]

After the undo, getMatParam().findNameIndex() [which uses material.getParams()] returns a negative value, yet getMatParam().isSelected() [which looks only at selectedName] returns true.

[stephengold]

The paramValues map in Material has only 8 entries and does not contain one for "Ambient". Material is Cloneable but not JmeCloneable. Material.clone() is invoked during the MP delete (both for Jaime and SkyControl) and appears to clone paramValues correctly.

[stephengold]

Note that History.undo() invokes Cgm.clone() 4x: cloning source and target for both new Checkpoint and previous.restore(). The issue is presumably during restore() of the target.

[stephengold]

When the first checkpoint is created, it reports the VarType as Vector4. The same checkpoint is later restored, but at that time it reports the VarType as null. In fact, it's the same SelectedMatParam instance and the same Material instance from when the checkpoint was created. Looks like the Material got aliased somewhere.

[stephengold]

Geometry.cloneFields() sure looks like it clones the material field...

[stephengold]

Looks like Cgm.clone() fails to update a few backpointers. This might be an easy fix!

[stephengold]

Fixed in "master" at 5aff82e

Well, that kept me entertained for a few hours...