diff --git a/src/infrastructure/customfield/standard/PhabricatorStandardCustomFieldPHIDs.php b/src/infrastructure/customfield/standard/PhabricatorStandardCustomFieldPHIDs.php
--- a/src/infrastructure/customfield/standard/PhabricatorStandardCustomFieldPHIDs.php
+++ b/src/infrastructure/customfield/standard/PhabricatorStandardCustomFieldPHIDs.php
@@ -40,6 +40,9 @@
     // TODO: Clean this up.
 
     $result = array();
+    if ($value === null) {
+      return $this;
+    }
     if (!is_array($value)) {
       $value = json_decode($value, true);
       if (is_array($value)) {