Thank you for this tutorial.
However, you made a small but significant typo in your ASM json file which crashes the game.
The key "start-state" should actually be "start_state" as annotated in AnimationStateMachine.java:74.
@SerializedName("start_state")
private final String startState;
It took me quite a while to figure out what's wrong, because this kind of typo is particularly hard to notice.