java.lang.NullPointerException
at mygame.Main.simpleInitApp(Main.java:40)
at com.jme3.app.SimpleApplication.initialize(SimpleApplication.java:239)
at com.jme3.system.lwjgl.LwjglAbstractDisplay.initInThread(LwjglAbstractDisplay.java:130)
at com.jme3.system.lwjgl.LwjglAbstractDisplay.run(LwjglAbstractDisplay.java:211)
at java.base/java.lang.Thread.run(Thread.java:834)
Probably the model has the new style of animation control and the tutorial is still using the old style. Hard to say for sure with the limited information provided.
Newer versions of JME got a new animation system that is way more flexible. Most but not all of the features were ported over to the new system but I think the tutorials have not been converted. (And the features that didn’t get ported it’s because the paradigm is different enough that they didn’t necessarily make sense anymore and/or were too difficult to port ‘as is’.)