ENH: improve idempotency in distutils.build_ext.finalize_options

Author: neutrinoceros

setuptools/_distutils/command/build_ext.py

@@ -276,7 +276,7 @@ def finalize_options(self) -> None:  # noqa: C901
         if self.undef:
             self.undef = self.undef.split(',')
 
-        if self.swig_opts is None:
+        if not self.swig_opts:
             self.swig_opts = []
         else:
             self.swig_opts = self.swig_opts.split(' ')