func (n *NullEventReceiver) EventErrKv(eventName string, err error, kvs map[string]string) error {
	return err
}
EventErrKv receives a notification of an error if one occurs along with
optional key/value data
package dbr
type EventReceiver interface {
	Event(eventName string)
	EventKv(eventName string, kvs map[string]string)
	EventErr(eventName string, err error) error
	EventErrKv(eventName string, err error, kvs map[string]string) error
	Timing(eventName string, nanoseconds int64)
	TimingKv(eventName string, nanoseconds int64, kvs map[string]string)
}
type kvs map[string]string
var nullReceiver = &NullEventReceiver{}
type NullEventReceiver struct{}
func (n *NullEventReceiver) Event(eventName string) {}
func (n *NullEventReceiver) EventKv(eventName string, kvs map[string]string) {}
func (n *NullEventReceiver) EventErr(eventName string, err error) error { return err }