Remove all thumbnails when reloading the document, to avoid an exception. 
Remove all thumbnails when reloading the document, to avoid an exception. 
ycaihua/skim-app,ycaihua/skim-app,WoLpH/skim,WoLpH/skim,ycaihua/skim-app,WoLpH/skim,ycaihua/skim-app,WoLpH/skim,WoLpH/skim,ycaihua/skim-app