diff --git a/firebase-document.html b/firebase-document.html
index f498df6..2596c68 100644
--- a/firebase-document.html
+++ b/firebase-document.html
@@ -86,7 +86,7 @@
           reject(new Error('No app configured!'));
         }
 
-        if (key) {
+        if (typeof key !== 'undefined') {
           path = parentPath + '/' + key;
           resolve(this._setFirebaseValue(path, this.data));
         } else {