diff --git a/src/Issue/IssueField.php b/src/Issue/IssueField.php
index 81716fdc..6f505222 100644
--- a/src/Issue/IssueField.php
+++ b/src/Issue/IssueField.php
@@ -143,7 +143,7 @@ public function jsonSerialize()
 
         // if assignee property has empty value then remove it.
         // @see https://github.com/lesstif/php-jira-rest-client/issues/126
-        if ($this->assignee->isEmpty()) {
+        if (empty($this->assignee) || $this->assignee->isEmpty()) {
             unset($vars['assignee']);
         }