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
@@ -40,7 +40,7 @@
     // TODO: Clean this up.
 
     $result = array();
-    if (!is_array($value)) {
+    if (is_string($value) && phutil_nonempty_string($value)) {
       $value = json_decode($value, true);
       if (is_array($value)) {
         $result = array_values($value);