exclamation marks on null list items

[fargiolas]

Hi I'm trying to edit a yaml config file without messing with the original formatting. I'm loading it with

config, yaml_indent, yaml_block_seq_indent = ruamel.yaml.util.load_yaml_guess_indent(fp, preserve_quotes=True)

and dumping it with:

ruamel.yaml.round_trip_dump(config, fp, indent=yaml_indent, block_seq_indent=yaml_block_seq_indent)

everything looks fine except I a few lists with null elements which look like

list: ["a", "b", null, null, null]

in the original file but become in the edited one:

list: ["a", "b", !!null '', !!null'', !!null'']

Is this expected? any way to avoid it? I'd like to keep the file easy to read and modify by a human.

[fargiolas]

I was able to fix this forcing a representer for type(None)

    def represent_none(self, data):
        return self.represent_scalar('tag:yaml.org,2002:null', u'null')
    yaml.representer.add_representer(type(None), represent_none)

What's weird is that the very same representer is added in lib/ruyaml/representer.py to bouth round trip and safe dumper, so AFAIK it should work as expected without manually forcing it. Am I missing anything?