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

(cherry picked from commit 6fafc25aea8689048314b5bf7a9bb986bb1ce238)

Co-authored-by: andrei kulakov <andrei.avk@gmail.com>
diff --git a/Lib/argparse.py b/Lib/argparse.py
index ce4635a..f1f6f32 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -526,12 +526,13 @@ def _format_action(self, action):
         parts = [action_header]
 
         # if there was help for the action, add lines of help text
-        if action.help:
+        if action.help and action.help.strip():
             help_text = self._expand_help(action)
-            help_lines = self._split_lines(help_text, help_width)
-            parts.append('%*s%s\n' % (indent_first, '', help_lines[0]))
-            for line in help_lines[1:]:
-                parts.append('%*s%s\n' % (help_position, '', line))
+            if help_text:
+                help_lines = self._split_lines(help_text, help_width)
+                parts.append('%*s%s\n' % (indent_first, '', help_lines[0]))
+                for line in help_lines[1:]:
+                    parts.append('%*s%s\n' % (help_position, '', line))
 
         # or add a newline if the description doesn't end with one
         elif not action_header.endswith('\n'):