XWIKI-7966 Missing rest features for search and page listing needed for Mobile application.

Reviewing pull request

* Fixed a possible NPE.

xwiki-platform-core/xwiki-platform-rest/xwiki-platform-rest-server/src/main/java/org/xwiki/rest/resources/BaseSearchResult.java

@@ -178,10 +178,13 @@ protected List<SearchResult> searchPages(List<SearchScope> searchScopes, String
              * If the order field is already one of the field hard coded in the base query, then do not add it to the
              * select clause.
              */
-            String addColumn =
-                (orderField.equals("") || orderField.equals("fullName") || orderField.equals("name") || orderField
-                    .equals("space")) ? "" : ", doc." + orderField;
-
+            String addColumn = "";
+            if (!StringUtils.isBlank(orderField)) {
+                addColumn =
+                    (orderField.equals("") || orderField.equals("fullName") || orderField.equals("name") || orderField
+                        .equals("space")) ? "" : ", doc." + orderField;
+            }
+            
             if (space != null) {
                 f.format("select distinct doc.fullName, doc.space, doc.name, doc.language");
                 f.format(addColumn);