Some NoneType issue in simfile.mutate

[bjfranks]

Hey, so I was using your tool to save files with new difficulty ratings, and it worked for almost all of my files, except for ECFA 2021\MAX 300 (SX 12)\max 300.ssc, which gives me an AttributeError: 'NoneType' object has no attribute 'replace'. I suspect this is due to line 47 (which, btw, is also slightly broken) where gimmick=none. This is the first line that was not stored. Find a stack trace attached.
error.txt

[garcia]

Thank you for the report. Could you share the SSC file that caused the error?

[garcia]

Some more details, copied from #40:

msdparser returns a value of None when a parameter has no colon separator (e.g. #KEY;). This deserializes into a simfile object correctly, but attempting to serialize it back to a string throws an AttributeError:

File "/lib/python3.10/site-packages/simfile/_private/serializable.py", line 19, in __str__
self.serialize(serialized)
File "/lib/python3.10/site-packages/simfile/base.py", line 191, in serialize
file.write(f"{param}\n")
File "/lib/python3.10/site-packages/msdparser/parameter.py", line 87, in __str__
self.serialize(output, escapes=escapes)
File "/lib/python3.10/site-packages/msdparser/parameter.py", line 80, in serialize
file.write(MSDParameter.serialize_component(component, escapes=escapes))
File "/lib/python3.10/site-packages/msdparser/parameter.py", line 57, in serialize_component
return reduce(
File "/lib/python3.10/site-packages/msdparser/parameter.py", line 58, in <lambda>
lambda key, esc: key.replace(esc, f"\\{esc}"),
AttributeError: 'NoneType' object has no attribute 'replace'