check if object is null

src/libpoketube/libpoketube-core.js

@@ -37,12 +37,16 @@ function getJson(str) {
 }
 
 function checkUnexistingObject(obj) {
+  if (obj !== null) {
+    if (obj.authorId !== null) {
       if (obj !== undefined) {
         if (obj.authorId !== undefined) {
           return true;
         }
       }
     }
+  }
+}
 
 /*
  * Api functions