Index: src/main/java/org/apache/jackrabbit/oak/jcr/observation/ObservationManagerImpl.java
===================================================================
--- src/main/java/org/apache/jackrabbit/oak/jcr/observation/ObservationManagerImpl.java	(revision 1875146)
+++ src/main/java/org/apache/jackrabbit/oak/jcr/observation/ObservationManagerImpl.java	(working copy)
@@ -388,10 +388,16 @@
         return conditions;
     }
 
-    private static Set<String> getOakPaths(NamePathMapper mapper, String[] paths) {
+    private static Set<String> getOakPaths(NamePathMapper mapper, String[] paths)
+            throws RepositoryException {
         Set<String> oakPaths = newHashSet();
         for (String path : paths) {
-            oakPaths.add(mapper.getOakPath(path));
+            String oakPath = mapper.getOakPath(path);
+            if (oakPath != null) {
+                oakPaths.add(oakPath);
+            } else {
+                throw new RepositoryException("Invalid path: " + path);
+            }
         }
         return oakPaths;
     }