Update app.py

app.py

@@ -23,7 +23,7 @@ species_to_imgpath = {'bird': './descendent_specific_topk=10_heatmap_withbb_ep=l
 
 # this has to be there for each species
 imgname_to_filepath = {} # this ignores the extension such as .png
-nodename_to_protoIDs = defaultdict()
+nodename_to_protoIDs = defaultdict(list)
 
 for species, imgpath in species_to_imgpath.items():
     for foldername in os.listdir(imgpath):