I was given a folder of .sid, .sdw, and .sid.aux.xml files to use as tiles on our map. I'm pretty sure I can use ImageMosaic for this and have followed the doc at http://docs.geoserver.org/stable/en/user/tutorials/image_mosaic_plugin/imagemosaic.html. When I get to the step to add a Store and click save, I get the error "Could not list layers for this store, an error occurred retrieving them: Argument "value" should not be null." What can I do to fix this? Thanks!