Fix handling of the incoming JSON request

feedbackloop/views.py

@@ -26,7 +26,9 @@ def by_sender(sender):
 
 @app.route('/api/by_sender', methods=('POST',))
 def api_by_sender():
-    sender = request.json.sender
+    sender = request.json.get('sender')
+    if not sender:
+        abort(400)
     reports = FeedbackEntry.query.filter(
         FeedbackEntry.sender == sender).order_by(
             FeedbackEntry.timestamp.desc())