code: func (elt ZeroIsNullMeddler) PostRead(fieldAddr, scanTarget interface{}) error {
  	sv := reflect.ValueOf(scanTarget)
  	fv := reflect.ValueOf(fieldAddr)
  	if sv.Elem().IsNil() {
  		// null column, so set target to be zero value
  		fv.Elem().Set(reflect.Zero(fv.Elem().Type()))
  	} else {
  		// copy the value that scan found
  		fv.Elem().Set(sv.Elem().Elem())
  	}
  	return nil
  }
docs: // PostRead is called after a Scan operation for fields that have the ZeroIsNullMeddler