Thanks to @apollo13 for reporting this in #10101.

Is “@ namespace” sensible? 🧐

Namespaces are set-up in Nomad to be an object that has an id property.
However, namespaces actually don't have that shape. Our search was expecting
a namespace object, but we actually don't have a namespace assigned to jobs
in our config and namespace is set to null. Normally, these namespaces would
be set to default, but that would require us to refactor our Mirage config
if we wanted to assert that namespaces are 'default' and not null. So this is
a bandaid solution.