Seems like on chrome when cancel is hit in the file chooser, the 'changed' event is fired and startUpload() was being called. We need to check to see if the upload file is blank and - if so - just return immediately out of the function

cms/djangoapps/contentstore/views/assets.py

@@ -103,6 +103,9 @@ def upload_asset(request, org, course, coursename):
         logging.error('Could not find course' + location)
         return HttpResponseBadRequest()
 
+    if 'file' not in request.FILES:
+        return HttpResponseBadRequest()
+
     # compute a 'filename' which is similar to the location formatting, we're using the 'filename'
     # nomenclature since we're using a FileSystem paradigm here. We're just imposing
     # the Location string formatting expectations to keep things a bit more consistent

cms/static/js/base.js

@@ -411,8 +411,12 @@ function showFileSelectionMenu(e) {
 }
 
 function startUpload(e) {
+    file_input = $('.file-input').val().replace('C:\\fakepath\\', '');
+    if (file_input === '')
+        return;
+
     $('.upload-modal h1').html(gettext('Uploading…'));
-    $('.upload-modal .file-name').html($('.file-input').val().replace('C:\\fakepath\\', ''));
+    $('.upload-modal .file-name').html(file_input);
     $('.upload-modal .file-chooser').ajaxSubmit({
         beforeSend: resetUploadBar,
         uploadProgress: showUploadFeedback,