1 files changed, 2 insertions, 1 deletions
diff --git a/src/Angular.js b/src/Angular.js
index 589929a4..746f1134 100644
--- a/src/Angular.js
+++ b/src/Angular.js
@@ -775,9 +775,10 @@ function toJsonReplacer(key, value) {
  *
  * @param {Object|Array|Date|string|number} obj Input to be serialized into JSON.
  * @param {boolean=} pretty If set to true, the JSON output will contain newlines and whitespace.
- * @returns {string} Jsonified string representing `obj`.
+ * @returns {string|undefined} Jsonified string representing `obj`.
  */
 function toJson(obj, pretty) {
+  if (typeof obj === 'undefined') return undefined;
   return JSON.stringify(obj, toJsonReplacer, pretty ? '  ' : null);
 }