Fix setLogfile method to handle None path

[liangbug]

No description provided.

[Opt-Mucca]

Could this not be accomplished with the following code?

if path is not None:
    c_path = str_conversion(path)
else:
    c_path = NULL
SCIPset.......

[Joao-Dionisio]

Or even

c_path = str_conversion(path) if path else NULL
SCIPset ...

If we want to keep the same syntax.

But the PR looks good to me overall. It's just missing a test and an entry in the CHANGELOG @liangbug, and possibly one of these suggestions we made.

[Opt-Mucca]

I like the suggestion of @Joao-Dionisio !

[liangbug]

I added unittest and changelog.

@Joao-Dionisio, @Opt-Mucca, The follownng codes would cause compiling error.

if path is not None:
    c_path = str_conversion(path)
else:
    c_path = NULL
SCIPset.......

c_path = str_conversion(path) if path else NULL
SCIPset ...

Error compiling Cython file:
src\pyscipopt\scip.pxi:4914:21: Cannot convert 'void *' to Python object

Or you prefer the following code instead.

if path:
    c_path = str_conversion(path)
    SCIPsetMessagehdlrLogfile(self._scip, c_path)
else:
    SCIPsetMessagehdlrLogfile(self._scip, NULL)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 52.81%. Comparing base (1f858fe) to head (f13c198).

❗ Current head f13c198 differs from pull request most recent head e14edbe. Consider uploading reports for the commit e14edbe to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #813      +/-   ##
==========================================
+ Coverage   51.85%   52.81%   +0.96%     
==========================================
  Files          18       17       -1     
  Lines        3890     3834      -56     
==========================================
+ Hits         2017     2025       +8     
+ Misses       1873     1809      -64     

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[Opt-Mucca]

@liangbug I'd prefer the code you suggested!

[liangbug]

@Opt-Mucca, I commited the code

if path:
    c_path = str_conversion(path)
    SCIPsetMessagehdlrLogfile(self._scip, c_path)
else:
    SCIPsetMessagehdlrLogfile(self._scip, NULL)

[mmghannam]

Thanks @liangbug for your contribution!