The CKEditor fails to load sporadically if the teaser of the node is empty

I had a node created with firefox that I wanted to update using Safari. When opening the node in edit mode in Safari, the ckeditor toolbar was not visible. I only had the textarea with the "switch to plain text editor" link below. The link was not working either. Using the code inspector of Safari, I found out that there was a javascript error in the file /ckeditor/include/ckeditor.utils.js at the line 44:

var tv = teaser.textarea.val();
    if (tv.length > 0) {
      $("#" + textarea_id).val(tv + '\n<!--break-->\n' + $("#" + textarea_id).val());

The variable tv in my case was undefined. I have just added a validation in the if section to make it work again in Safari:

var tv = teaser.textarea.val();
    if (tv && tv.length > 0) {
      $("#" + textarea_id).val(tv + '\n<!--break-->\n' + $("#" + textarea_id).val());