diff --git a/src/applications/harbormaster/step/HarbormasterLeaseHostBuildStepImplementation.php b/src/applications/harbormaster/step/HarbormasterLeaseHostBuildStepImplementation.php
--- a/src/applications/harbormaster/step/HarbormasterLeaseHostBuildStepImplementation.php
+++ b/src/applications/harbormaster/step/HarbormasterLeaseHostBuildStepImplementation.php
@@ -18,7 +18,7 @@
     $settings = $this->getSettings();
 
     $custom_attributes = DrydockCustomAttributes::parse(
-      $settings['attributes']);
+      idx($settings, 'attributes', ''));
 
     // Create the lease.
     $lease = id(new DrydockLease())