Index: applications/editors/josm/plugins/utilsplugin2/src/org/openstreetmap/josm/plugins/utilsplugin2/replacegeometry/ReplaceGeometryUtils.java
===================================================================
--- applications/editors/josm/plugins/utilsplugin2/src/org/openstreetmap/josm/plugins/utilsplugin2/replacegeometry/ReplaceGeometryUtils.java	(revision 31040)
+++ applications/editors/josm/plugins/utilsplugin2/src/org/openstreetmap/josm/plugins/utilsplugin2/replacegeometry/ReplaceGeometryUtils.java	(revision 31072)
@@ -117,5 +117,10 @@
         // FIXME: handle different layers
         List<Command> commands = new ArrayList<>();
-        commands.add(MergeNodesAction.mergeNodes(Main.main.getEditLayer(), Arrays.asList(subjectNode, referenceNode), referenceNode));
+        Command c = MergeNodesAction.mergeNodes(Main.main.getEditLayer(), Arrays.asList(subjectNode, referenceNode), referenceNode);
+        if (c == null) {
+            // User canceled
+            return null;
+        }
+        commands.add(c);
 
         return new ReplaceGeometryCommand(