Issue links API fails when an issue is linked to a work item epic

From Slack:

@cmiskell ITK that /api/:version/projects/:id/issues/:issue_iid/links is throwing 500s on .com? Logs:

undefined method `namespace' for nil:NilClass

          with_options if: ->(issue, _) { issue.project.namespace.group_namespace? && issue.project.namespace.feature_available?(:epics) } do