I have a geodatabase with thousands of grid features. I'm trying to dissolve and append these to a single dataset. I've tried iterating through the feature classes, but after spinning for a while the script keeps returning AttributeError: 'NoneType' object has no attribute 'group' when I try to list the feature classes. I have another nearly identical gdb that does not have this issue. Is there a way to figure out if there is a corrupted feature class, or if the gdb is corrupted?