diff --git a/src/Model/Model_PDF.php b/src/Model/Model_PDF.php
index 56348ca62..412059ab4 100644
--- a/src/Model/Model_PDF.php
+++ b/src/Model/Model_PDF.php
@@ -2503,7 +2503,11 @@ function( $item ) use ( $form ) {
 	 */
 	public function gp_populate_anything_hydrate_form( $form, $entry ) {
 		static $cache = [];
-		$key          = $form['id'] . $entry['id'];
+
+		$form_id  = $form['id'] ?? '';
+		$entry_id = $entry['id'] ?? '';
+
+		$key = $form_id . $entry_id;
 
 		if ( isset( $cache[ $key ] ) ) {
 			return $cache[ $key ];