bpo-24444: fix an error in argparse help when help for an option is blank (GH-28050) (GH-28931)

(cherry picked from commit 6fafc25aea)

Co-authored-by: andrei kulakov <andrei.avk@gmail.com>

Lib/test/test_argparse.py

@@ -2145,6 +2145,42 @@ def test_help_non_breaking_spaces(self):
                               wrap\N{NO-BREAK SPACE}at non-breaking spaces
         '''))
 
+    def test_help_blank(self):
+        # Issue 24444
+        parser = ErrorRaisingArgumentParser(
+            prog='PROG', description='main description')
+        parser.add_argument(
+            'foo',
+            help='    ')
+        self.assertEqual(parser.format_help(), textwrap.dedent('''\
+            usage: PROG [-h] foo
+
+            main description
+
+            positional arguments:
+              foo         
+
+            options:
+              -h, --help  show this help message and exit
+        '''))
+
+        parser = ErrorRaisingArgumentParser(
+            prog='PROG', description='main description')
+        parser.add_argument(
+            'foo', choices=[],
+            help='%(choices)s')
+        self.assertEqual(parser.format_help(), textwrap.dedent('''\
+            usage: PROG [-h] {}
+
+            main description
+
+            positional arguments:
+              {}          
+
+            options:
+              -h, --help  show this help message and exit
+        '''))
+
     def test_help_alternate_prefix_chars(self):
         parser = self._get_parser(prefix_chars='+:/')
         self.assertEqual(parser.format_usage(),