diff --git a/src/JsonMapperHelper.php b/src/JsonMapperHelper.php
index 924154c2..355867f5 100644
--- a/src/JsonMapperHelper.php
+++ b/src/JsonMapperHelper.php
@@ -17,7 +17,7 @@ public static function setUndefinedProperty($object, $propName, $jsonValue)
     {
         // If the property is a custom field type, assign a value to the custom Fields array.
         if (substr($propName, 0, 12) == 'customfield_') {
-            if (!empty($jsonValue)) {
+            if (!is_null($jsonValue)) {
                 $object->{$propName} = $jsonValue;
                 $object->customFields[$propName] = $jsonValue;
             }