XWIKI-10100: TRANSPORT_ERROR with SSO in tree view

 * avoid the NPE if the credentials are null

xwiki-platform-core/xwiki-platform-rest/xwiki-platform-rest-server/src/main/java/org/xwiki/rest/internal/XWikiSecretVerifier.java

@@ -68,7 +68,8 @@ public boolean verify(String identifier, char[] secret) throws IllegalArgumentEx
         XWiki xwiki = Utils.getXWiki(this.componentManager);
 
         try {
-            Principal principal = xwiki.getAuthService().authenticate(identifier, new String(secret), xwikiContext);
+            Principal principal = (secret == null) ? null : xwiki.getAuthService().authenticate(identifier,
+                    new String(secret), xwikiContext);
             if (principal != null) {
                 String xwikiUser = principal.getName();