disable 'Undo' in Ckeditor first time when data is set into editor

I want to disable undo the first time data is set into CKEditor. When data is set for the first time, undo gets activated and when I click undo 'undefined' comes in the editor on clicking undo 2nd-time text area gets cleared. not sure why 'undefined' comes on doing undo. Any help? Thanks in advance.