Comment 2 for bug 1001092

In 5.3 it was fixed by adding this to Cached_item_field::cmp :

 /*
    If value is not null and value changed (from null to not null or
    becasue of value change), then copy the new value to buffer.
    */
  if (! null_value && (tmp || (tmp= (field->cmp(buff) != 0))))
    field->get_image(buff,length,field->charset());