I managed to hit an exception by running a build plan that didn't have any repositories under "Also Clone".
```
josh@ip-10-63-53-226:/usr/src/phabricator$ ./bin/harbormaster build REDACTED --plan 3
Applying plan 3 to new buildable B13222...
https://phabricator.freelancer.com/B13222
[2015-10-30 17:21:09] EXCEPTION: (InvalidArgumentException) Argument 1 passed to DrydockLease::setAllowedBlueprintPHIDs() must be of the type array, null given, called in /usr/src/phabricator/src/applications/harbormaster/step/HarbormasterLeaseWorkingCopyBuildStepImplementation.php on line 51 and defined at [<phutil>/src/error/PhutilErrorHandler.php:200]
arcanist(head=master, ref.master=baf5eb8a8795), phabricator(head=master, ref.master=724f6ddda58d), phlab(head=master, ref.master=cd07327495c5), phutil(head=master, ref.master=59f5a8d2bb82)
#0 <#2> PhutilErrorHandler::handleError(integer, string, string, integer, array) called at [<phabricator>/src/applications/drydock/storage/DrydockLease.php:399]
#1 <#2> DrydockLease::setAllowedBlueprintPHIDs(NULL) called at [<phabricator>/src/applications/harbormaster/step/HarbormasterLeaseWorkingCopyBuildStepImplementation.php:51]
#2 <#2> HarbormasterLeaseWorkingCopyBuildStepImplementation::execute(HarbormasterBuild, HarbormasterBuildTarget) called at [<phabricator>/src/applications/harbormaster/worker/HarbormasterTargetWorker.php:64]
#3 phlog(InvalidArgumentException) called at [<phabricator>/src/applications/harbormaster/worker/HarbormasterTargetWorker.php:93]
#4 PhabricatorWorker::scheduleTask(string, array) called at [<phabricator>/src/applications/harbormaster/engine/HarbormasterBuildEngine.php:84]
#5 HarbormasterBuildEngine::continueBuild() called at [<phabricator>/src/applications/harbormaster/worker/HarbormasterBuildWorker.php:25]
#6 HarbormasterBuildWorker::doWork() called at [<phabricator>/src/infrastructure/daemon/workers/PhabricatorWorker.php:161]
#7 PhabricatorWorker::scheduleTask(string, array) called at [<phabricator>/src/applications/harbormaster/storage/HarbormasterBuildable.php:181]
#8 HarbormasterBuildable::applyPlan(HarbormasterBuildPlan, array) called at [<phabricator>/src/applications/harbormaster/management/HarbormasterManagementBuildWorkflow.php:101]
#9 HarbormasterManagementBuildWorkflow::execute(PhutilArgumentParser) called at [<phutil>/src/parser/argument/PhutilArgumentParser.php:406]
#10 PhutilArgumentParser::parseWorkflowsFull(array) called at [<phutil>/src/parser/argument/PhutilArgumentParser.php:301]
#11 PhutilArgumentParser::parseWorkflows(array) called at [<phabricator>/scripts/setup/manage_harbormaster.php:21]
Done.
```