Implement From<Option> for BoltType

[jifalops]

Query strings that use a placeholder $foo for an Option<Into<BoltType>> cannot be constructed without first knowing if the option is None. This is bothersome because basic query strings for a struct can be determined without self, but filling in query params requires a self.

This PR associates a query parameter of None to mean BoltType::Null(BoltNull).

Does this change semantics? Before this, removing a property on an entity could be done via SET n.prop = null, but now it could be done with SET n.prop = $prop. It allows a kind of silly Option<Vec<Option>> as a type.

Will serde support take care of this (there's a draft PR)?

[knutwalker]

Thanks for adding this. We want to slowly phase out BoltType as the main API for things and replace it with serde for query params as well, until then this is a good addition.

[ddnomad]

Any idea when this will be released?

[knutwalker]

I just mentioned this in another issue: #108 (comment)

Basically, since we are replacing the BoltType+(Try)From/Into based API with serde, I would like to not have anther release before the next one, which switches to serde. Can give a timeline for when that happens though. Could you use a git dependency in the meantime?

[ddnomad]

I just mentioned this in another issue: #108 (comment)

Basically, since we are replacing the BoltType+(Try)From/Into based API with serde, I would like to not have anther release before the next one, which switches to serde. Can give a timeline for when that happens though. Could you use a git dependency in the meantime?

Thanks for replying! Yep, this is fine, I've vendored this lib in for now, staying tuned for a new release!

[knutwalker]

We now have a pre-release 0.7.0-rc.1 out with this change and others.