mysqli class joshcam error in insert function

Question

I am using joshcam/PHP-MySQLi-Database-Class library and I am getting error in insert function while I am trying to insert data using an array Error message: Fatal error: Call to undefined method SimpleXMLElement::getSubQuery() in ../MysqliDb.php on line 548. Will anybody tell me how to fix it?

My code is here

 $db->where("project_id", $data_project['project_id']);
                   $tmp = $db->getOne("projects");
               if(count($tmp))
                    {
                        $data = array(  "project_name" => $data_project['project_name'],
                                        "project_url" => $data_project['project_url'],
                                        "project_details" => $data_project['project_details']
                        );
                        $db->where('project_id', $data_project['project_id']);
                        $id = $db->update('projects',$data);
                    }
                    else
                    {
                        $data = array("project_id" => $data_project['project_id'],
                                        "user_id" => 1,
                                        "project_name" => $data_project['project_name'],
                                        "project_url" => $data_project['project_url'],`enter code here`
                                        "project_details" => $data_project['project_details']
                        );
                        $id = $db->insert('projects',$data);