Issue #23356: Simplify convert_arg_line_to_args example.

Patch by py.user.

Doc/library/argparse.rst

@@ -1948,10 +1948,7 @@ Customizing file parsing
    as an argument::
 
     def convert_arg_line_to_args(self, arg_line):
-        for arg in arg_line.split():
+        return arg_line.split()
-            if not arg.strip():
-                continue
-            yield arg
 
 
 Exiting methods