diff --git a/backend/utils.js b/backend/utils.js
index 48410ff..ca02551 100644
--- a/backend/utils.js
+++ b/backend/utils.js
@@ -223,7 +223,7 @@ exports.deleteJSONFile = (file_path, type) => {
 
 exports.durationStringToNumber = (dur_str) => {
     if (typeof dur_str === 'number') return dur_str;
-    if (typeof dur_str === 'undefined') return 0;
+    if (typeof dur_str === 'undefined' || typeof dur_str === 'null') return 0;
     let num_sum = 0;
     const dur_str_parts = dur_str.split(':');
     for (let i = dur_str_parts.length-1; i >= 0; i--) {