Save empty spectrum list as empty file

[niekdejonge]

Currently, empty lists of spectra are just not saved (at least for mgf).

This is unexpected behavior to me, I would expect an empty file to be generated that when opened results in an empty list again.

So this would mean just adding a line like:

open(file_name, 'w').close()

to each save_spectra function.

This would only make sense if loading empty spectra files results in empty lists (or generators), which I am not sure of.

[hechth]

I think it would make sense to either raise an exception or write it to the logger - just silently writing an empty file sounds like a source for errors.
I agree that creating an empty file makes sense for pipelines which for example always expect an output - so I'd go with the logging version and write it to the WARNING level.

[niekdejonge]

Adding a warning would make sense to me as well

[niekdejonge]

If we add this, the load_from_mgf() function should also return an empty list if an empty file is given (this should reduce the risk for errors)