Index: jackrabbit-core/src/test/java/org/apache/jackrabbit/api/security/user/UserManagerCreateUserTest.java
===================================================================
--- jackrabbit-core/src/test/java/org/apache/jackrabbit/api/security/user/UserManagerCreateUserTest.java	(revision 1469826)
+++ jackrabbit-core/src/test/java/org/apache/jackrabbit/api/security/user/UserManagerCreateUserTest.java	(working copy)
@@ -156,10 +156,8 @@
             Principal p = getTestPrincipal();
             User user = createUser(p.getName(), null);
             createdUsers.add(user);
-
-            fail("A User cannot be built with 'null' password");
         } catch (Exception e) {
-            // ok
+            fail("Could not create a user with 'null' password");
         }
     }
 
Index: jackrabbit-core/src/test/java/org/apache/jackrabbit/core/security/user/UserImplTest.java
===================================================================
--- jackrabbit-core/src/test/java/org/apache/jackrabbit/core/security/user/UserImplTest.java	(revision 1469826)
+++ jackrabbit-core/src/test/java/org/apache/jackrabbit/core/security/user/UserImplTest.java	(working copy)
@@ -179,12 +179,11 @@
     public void testChangePasswordNull() throws RepositoryException {
         User u = (User) userMgr.getAuthorizable(uID);
 
-        // invalid 'null' pw string
+        // 'null' pw string is allowed for system-only users
         try {
             u.changePassword(null);
-            fail("invalid pw null");
         } catch (Exception e) {
-            // success
+            fail("change pw to 'null' failed");
         }
     }
 
Index: jackrabbit-core/src/main/resources/org/apache/jackrabbit/core/nodetype/builtin_nodetypes.cnd
===================================================================
--- jackrabbit-core/src/main/resources/org/apache/jackrabbit/core/nodetype/builtin_nodetypes.cnd	(revision 1469826)
+++ jackrabbit-core/src/main/resources/org/apache/jackrabbit/core/nodetype/builtin_nodetypes.cnd	(working copy)
@@ -603,7 +603,7 @@
   - rep:impersonators (STRING) protected multiple
 
 [rep:User] > rep:Authorizable, rep:Impersonatable
-  - rep:password (STRING) protected mandatory
+  - rep:password (STRING) protected
   - rep:disabled (STRING) protected
 
 [rep:Group] > rep:Authorizable
Index: jackrabbit-core/src/main/java/org/apache/jackrabbit/core/security/user/UserManagerImpl.java
===================================================================
--- jackrabbit-core/src/main/java/org/apache/jackrabbit/core/security/user/UserManagerImpl.java	(revision 1469826)
+++ jackrabbit-core/src/main/java/org/apache/jackrabbit/core/security/user/UserManagerImpl.java	(working copy)
@@ -737,7 +737,8 @@
      */
     void setPassword(NodeImpl userNode, String password, boolean forceHash) throws RepositoryException {
         if (password == null) {
-            throw new IllegalArgumentException("Password may not be null.");
+            // Allow 'null' password for system-only users that cannot login
+            return;
         }
         String pwHash;
         if (forceHash || PasswordUtility.isPlainTextPassword(password)) {