Merge #12353: argparse now correctly handles null argument values.

Patch by Torsten Landschoff.

Lib/argparse.py

@@ -1979,7 +1979,7 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
         for arg_string in arg_strings:
 
             # for regular arguments, just add them back into the list
-            if arg_string[0] not in self.fromfile_prefix_chars:
+            if not arg_string or arg_string[0] not in self.fromfile_prefix_chars:
                 new_arg_strings.append(arg_string)
 
             # replace arguments referencing files with the file content

Lib/test/test_argparse.py

@@ -1372,6 +1372,7 @@ class TestArgumentsFromFile(TempDirMixin, ParserTestCase):
         ('X @hello', NS(a=None, x='X', y=['hello world!'])),
         ('-a B @recursive Y Z', NS(a='A', x='hello world!', y=['Y', 'Z'])),
         ('X @recursive Z -a B', NS(a='B', x='X', y=['hello world!', 'Z'])),
+        (["-a", "", "X", "Y"], NS(a='', x='X', y=['Y'])),
     ]
 
 

Misc/NEWS

@@ -52,6 +52,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #12353: argparse now correctly handles null argument values.
+
 - Issues #10017 and #14998: Fix TypeError using pprint on dictionaries with
   user-defined types as keys or other unorderable keys.