query --output build prints None labels as null

```
$ touch WORKSPACE
$ cat > BUILD
alias(
name = "t",
actual = select({":setting": ":a", "//conditions:default": None}),
)

config_setting(
name = "setting",
define_values = {"a": "1"},
)
$ bazel query --output build //:t
alias(
name = "t",
actual = select({"//:setting": "//:a", "//conditions:default": null}),
)
```

Reproduce the issue with the shown BUILD file and `bazel query --output build //:t`; start from the query command's build-output handling. The output should preserve the `None` label instead of emitting `null` for the default select value.

Written by the indexing model from the issue text.