From 32a38c4e7776d009f89f6567a2dc9436f06fb767 Mon Sep 17 00:00:00 2001
From: Florian Schmaus <flo@geekplace.eu>
Date: Sun, 22 Aug 2021 16:16:57 +0200
Subject: [PATCH] [core] Check if the successor vertex exists in
 StateDescriptorGraph

If the successor's module is disabled then the vertex may be null. In
this case, we can simple continue with the next successor in the list.

Previously, due to d33a5a23c32a ("[core] Introduce
Builder.failOnUnknownStates() and unit tests") this would trigger an
assert in addOutgoingEdge().

Fixes: d33a5a23c32a ("[core] Introduce Builder.failOnUnknownStates() and unit tests")
---
 .../java/org/jivesoftware/smack/fsm/StateDescriptorGraph.java | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/smack-core/src/main/java/org/jivesoftware/smack/fsm/StateDescriptorGraph.java b/smack-core/src/main/java/org/jivesoftware/smack/fsm/StateDescriptorGraph.java
index 35144f73a..41bb29f59 100644
--- a/smack-core/src/main/java/org/jivesoftware/smack/fsm/StateDescriptorGraph.java
+++ b/smack-core/src/main/java/org/jivesoftware/smack/fsm/StateDescriptorGraph.java
@@ -186,6 +186,10 @@ public class StateDescriptorGraph {
 
         for (GraphVertex<Class<? extends StateDescriptor>> successor : sortedSuccessors) {
             GraphVertex<StateDescriptor> successorVertex = successorStateDescriptors.get(successor.element);
+            if (successorVertex == null) {
+                // The successor does not exist, probably because its module was not enabled.
+                continue;
+            }
             node.addOutgoingEdge(successorVertex);
 
             // Recurse further.