KeyError: 'hosts'

[MyGitHub-G]

When I open a .mn file, error

Exception in Tkinter callback
Traceback (most recent call last):
File "/usr/lib/python3.8/tkinter/init.py", line 1892, in call
return self.func(*args)
File "miniedit.py", line 1486, in loadTopology
hosts = loadedTopology['hosts']
KeyError: 'hosts'

mininet v 2.3.1
OS：ubuntu 20.04.5