Index: /trunk/src/org/openstreetmap/josm/gui/dialogs/validator/ValidatorTreePanel.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/dialogs/validator/ValidatorTreePanel.java	(revision 11320)
+++ /trunk/src/org/openstreetmap/josm/gui/dialogs/validator/ValidatorTreePanel.java	(revision 11321)
@@ -436,12 +436,14 @@
     @Override public void primitivesRemoved(PrimitivesRemovedEvent event) {
         // Remove purged primitives (fix #8639)
-        for (TestError err : errors) {
-            try {
-                err.getPrimitives().removeAll(event.getPrimitives());
-            } catch (UnsupportedOperationException e) {
-                if (event.getPrimitives().containsAll(err.getPrimitives())) {
-                    err.getPrimitives().clear();
-                } else {
-                    Main.warn(e, "Unable to remove primitives from "+err+'.');
+        if (errors != null) {
+            for (TestError err : errors) {
+                try {
+                    err.getPrimitives().removeAll(event.getPrimitives());
+                } catch (UnsupportedOperationException e) {
+                    if (event.getPrimitives().containsAll(err.getPrimitives())) {
+                        err.getPrimitives().clear();
+                    } else {
+                        Main.warn(e, "Unable to remove primitives from "+err+'.');
+                    }
                 }
             }