why some_table.get_mut("xxx") returns Some(None)

[miaomiaowu0428]

as my title
If the dependency already exist, then I'll just modify the features, otherwise I'll add this dependency it's features

if let Some(dep) = dependencies.get_mut("some_dep") {
    dep["features"] = toml_edit::value(dep_features);
} else {
    let mut dep_table = toml_edit::table();
    dep_table["version"] = toml_edit::value("some version");
    dep_table["features"] = toml_edit::value(dep_features);
    dependencies["some_dep"] = dep_table;
}

then i found it always run the first branch because dependencies.get_mut("some_dep") returns Some(None) when the dependency is not exist
Is there a better way to do it?

[miaomiaowu0428]

this will solve

if dependencies.get("some_dep").is_none() {
    let mut dep_table= toml_edit::table();
    dep_table["version"] = toml_edit::value("some_version");
    dep_table["features"] = toml_edit::value(dep_feature);
    dependencies["some_dep"] = dep_table;
} else {
    dependencies["some_dep"]["features"] = toml_edit::value(dep_feature);
}

but I just wonder why Some(None) instead of None

[miaomiaowu0428]

ok, I found this:

    fn index_mut<'v>(&self, v: &'v mut Item) -> Option<&'v mut Item> {
        if let Item::None = *v {
            let mut t = InlineTable::default();
            t.items.insert(
                InternalString::from(self),
                TableKeyValue::new(Key::new(self), Item::None),
            );
            *v = value(Value::InlineTable(t));
        }
        match *v {
            Item::Table(ref mut t) => Some(t.entry(self).or_insert(Item::None)),
            Item::Value(ref mut v) => v.as_inline_table_mut().map(|t| {
                &mut t
                    .items
                    .entry(InternalString::from(self))
                    .or_insert_with(|| TableKeyValue::new(Key::new(self), Item::None))
                    .value
            }),
            _ => None,
        }
    }

I think it's because table["key"] = value should be supported