I'm not sure that sequence of events that causes this, but more than once I've gotten the following traceback.

Exception in Tkinter callback
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/tkinter/__init__.py", line 1705, in __call__
    return self.func(*args)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/idlelib/multicall.py", line 176, in handler
    r = l[i](event)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/idlelib/filelist.py", line 54, in close_all_callback
    reply = edit.close()
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/idlelib/editor.py", line 1017, in close
    self._close()
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/idlelib/pyshell.py", line 309, in _close
    EditorWindow._close(self)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/idlelib/editor.py", line 1021, in _close
    if self.io.filename:
AttributeError: 'NoneType' object has no attribute 'filename'