BinaryHeap NullPointerException

Issue details

In prev release 7 march (gdx-1.9.11-SNAPSHOT) my game worked fine

Reproduction steps/code

BinaryHeap<Node> bh = new BinaryHeap<Node>();
bh.add(new Node(5f));
Node node = new Node(10f);
bh.add(node);
bh.remove(node);
bh.remove(node);

Version of LibGDX and/or relevant dependencies

gdx-1.9.11-SNAPSHOT gdx-ai-1.8.2

Stacktrace

java.lang.NullPointerException: 
  at com.badlogic.gdx.utils.BinaryHeap.down (BinaryHeap.java:156)
  at com.badlogic.gdx.utils.BinaryHeap.remove (BinaryHeap.java:102)
  at com.badlogic.gdx.ai.pfa.indexed.IndexedAStarPathFinder.visitChildren (IndexedAStarPathFinder.java:219)
  at com.badlogic.gdx.ai.pfa.indexed.IndexedAStarPathFinder.search (IndexedAStarPathFinder.java:117)
  at com.badlogic.gdx.ai.pfa.indexed.IndexedAStarPathFinder.searchNodePath (IndexedAStarPathFinder.java:94)
  at com.tpwar.game.maps.pathfinding.TiledPathFinder.find (TiledPathFinder.java:29)
  at com.tpwar.game.screens.MapScreen$InputAdapterExtension.touchUp (MapScreen.java:741)
  at com.badlogic.gdx.InputMultiplexer.touchUp (InputMultiplexer.java:124)
  at com.badlogic.gdx.backends.android.AndroidInput.processEvents (AndroidInput.java:406)
  at com.badlogic.gdx.backends.android.AndroidGraphics.onDrawFrame (AndroidGraphics.java:476)
  at android.opengl.GLSurfaceView$GLThread.guardedRun (GLSurfaceView.java:1581)
  at android.opengl.GLSurfaceView$GLThread.run (GLSurfaceView.java:1280)

Please select the affected platforms

• Android
• iOS (robovm)
• iOS (MOE)
• HTML/GWT
• Windows
• Linux
• MacOS

[tommyettinger]

Yes! Not only can I confirm the bug, I can confirm a fix for the bug, and it only needs moving one line in BinaryHeap! The solution is to change, in BinaryHeap.remove(T):

			nodes[node.index] = moved;
			nodes[size] = null;

to

			nodes[size] = null;
			nodes[node.index] = moved;

I believe the issue happened when size and node.index were equal, so nodes[node.index] should have been moved but instead was null.

[NathanSweet]

Ah, that was tricky! Great find @tommyettinger!