Merge remote-tracking branch 'origin/master' into jetty-9.1

jetty-security/src/main/java/org/eclipse/jetty/security/MappedLoginService.java

@@ -212,6 +212,9 @@ public abstract class MappedLoginService extends AbstractLifeCycle implements Lo
      */
     public UserIdentity login(String username, Object credentials)
     {
+        if (username == null)
+            return null;
+        
         UserIdentity user = _users.get(username);
 
         if (user==null)

jetty-security/src/main/java/org/eclipse/jetty/security/authentication/DeferredAuthentication.java

@@ -117,6 +117,9 @@ public class DeferredAuthentication implements Authentication.Deferred
     @Override
     public Authentication login(String username, Object password, ServletRequest request)
     {
+        if (username == null)
+            return null;
+        
         UserIdentity identity = _authenticator.login(username, password, request);
         if (identity != null)
         {