We get:
```
Argument 1 passed to HarbormasterBuildTarget::attachBuildStep() must be an instance of HarbormasterBuildStep, null given, called in /srv/phabricator/phabricator/src/applications/harbormaster/query/HarbormasterBuildTargetQuery.php on line 93 and defined
```
when viewing a build whose build plan has had steps deleted. I'm not sure what the best course of action is here; maybe just displaying a message that says "This build has steps that have been deleted" or something of that nature and omitting any targets that are missing?