Optional subcommands fail with a KeyError

[carmocca]

from jsonargparse import ArgumentParser

parser = ArgumentParser()
subcommands = parser.add_subcommands(required=False)
subparser = ArgumentParser()
subcommands.add_subcommand('foo', subparser)
parser.parse_args()

When called with no subcommand, prints:

Error: None

After some debugging, I found two issues:

(1):

jsonargparse/jsonargparse/actions.py

Line 767 in e7ab0f3

subparser = action._name_parser_map[subcommand]

should be replaced with

        subparser = action._name_parser_map.get(subcommand)
        if subparser is None:
            return

(2):

KeyErrors should not be catched here:

jsonargparse/jsonargparse/core.py

Lines 396 to 397 in e7ab0f3

	except (TypeError, KeyError) as ex:
	self.error(str(ex), ex)

which hides the original exception when it seems to be an actual bug:

Traceback (most recent call last):
  File "/Users/carlosmocholi/Library/Application Support/JetBrains/PyCharmCE2020.3/scratches/scratch_12.py", line 8, in <module>
    parser.parse_args()
  File "/Users/carlosmocholi/.pyenv/versions/3.9.1/envs/lightning-3.9/lib/python3.9/site-packages/jsonargparse/core.py", line 385, in parse_args
    parsed_cfg = self._parse_common(
  File "/Users/carlosmocholi/.pyenv/versions/3.9.1/envs/lightning-3.9/lib/python3.9/site-packages/jsonargparse/core.py", line 308, in _parse_common
    _ActionSubCommands.handle_subcommands(self, cfg, env=env, defaults=defaults, fail_no_subcommand=fail_no_subcommand)
  File "/Users/carlosmocholi/.pyenv/versions/3.9.1/envs/lightning-3.9/lib/python3.9/site-packages/jsonargparse/actions.py", line 767, in handle_subcommands
    subparser = action._name_parser_map[subcommand]
KeyError: None

[mauvilsa]

The fix is now in master.