fixed acl query builder generate block - filter null values

SE/se-lib/AclQueryBuilder.php

@@ -118,6 +118,7 @@ class AclQueryBuilder {
   }
   public function _generateWhereBlock($where) { // @returns string
     list($fieldName, $sqlGlue, $list) = $where;
+    $list = array_filter($list, function ($value) { return null !== $value; });
     $sqlList = array_filter(
       array_map([$this, '_generateWhereMain'], $list),
       'is_string'