Tiles that do not exist, can we return blank tiles

Currently, when opening http://maps.massgis.state.ma.us/map_ol_tile/oliver.php 
there is white space on either the left and right or the top and bottom 
(depending on the size and dimensions of the browser window) where there are no 
tiles (we haven't generated tiles for those areas that are "off the map" 
outside our area of interest).  That looks OK, but if we uncheck a tileset such 
as Structures and then recheck it again in the "Available Datalayers" window 
broken icon pictures show on the map. 

If I uncheck and recheck Detailed Features only the broken icons appear on the 
edge.  If I uncheck and recheck Structures they appear all over the map.  See 
attached screenshots.  Charlton suggests - is there a way in the Python code to 
return an empty image if does not exist?

Original issue reported on code.google.com by Aleda.Fr...@state.ma.us on 7 Jan 2013 at 8:11

Attachments:

oliver_tile_view_default.gif
oliver_tile_view_after_tax_parcels_unchecked_checked.gif
oliver_tile_view_after_structures_unchecked_checked.gif

nakijun / morisoliver

Tiles that do not exist, can we return blank tiles #201