# Description
Before this PR, `to msgpack`/`to msgpackz` and `to json` serialize
closures as `nil`/`null` respectively, when the `--serialize` option
isn't passed. This PR makes it an error to serialize closures to msgpack
or JSON without the `--serialize` flag, which is the behavior of `to
nuon`.
This PR also adds the `--serialize` flag to `to msgpack`.
This PR also changes `to nuon` and `to json` to return an error if they
cannot find the block contents of a closure, rather than serializing an
empty string or an error string, respectively. This behavior is
replicated for `to msgpack`.
It also changes `to nuon`'s error message for serializing closures
without `--serialize` to be the same as the new errors for `to json` and
`to msgpack`.
# User-Facing Changes
* Add `--serialize` flag to `to msgpack`, similar to the `--serialize`
flag for `to nuon` and `to json`.
* Serializing closures to JSON or msgpack without `--serialize`
Partially fixes#11738
