Refactor Distribution.files to use pass_none to handle a None value from _read_files*.

Author: jaraco

importlib_metadata/__init__.py

@@ -21,7 +21,7 @@
     install,
     pypy_partial,
 )
-from ._functools import method_cache
+from ._functools import method_cache, pass_none
 from ._itertools import always_iterable, unique_everseen
 from ._meta import PackageMetadata, SimplePath
 
@@ -635,7 +635,6 @@ def files(self):
         missing.
         Result may be empty if the metadata exists but is empty.
         """
-        file_lines = self._read_files_distinfo() or self._read_files_egginfo()
 
         def make_file(name, hash=None, size_str=None):
             result = PackagePath(name)
@@ -644,7 +643,11 @@ def make_file(name, hash=None, size_str=None):
             result.dist = self
             return result
 
-        return file_lines and list(starmap(make_file, csv.reader(file_lines)))
+        @pass_none
+        def make_files(lines):
+            return list(starmap(make_file, csv.reader(lines)))
+
+        return make_files(self._read_files_distinfo() or self._read_files_egginfo())
 
     def _read_files_distinfo(self):
         """

importlib_metadata/_functools.py

@@ -83,3 +83,22 @@ def wrapper(self, *args, **kwargs):
     wrapper.cache_clear = lambda: None
 
     return wrapper
+
+
+# From jaraco.functools 3.3
+def pass_none(func):
+    """
+    Wrap func so it's not called if its first param is None
+
+    >>> print_text = pass_none(print)
+    >>> print_text('text')
+    text
+    >>> print_text(None)
+    """
+
+    @functools.wraps(func)
+    def wrapper(param, *args, **kwargs):
+        if param is not None:
+            return func(param, *args, **kwargs)
+
+    return wrapper