Everyone should always be continually improving and looking for ways to expand their knowledge and skillset.  This is a precarious situation.  However, all is not lost.  I would heed the advice above and not say anything.  However, go into your evaluation with documentation of your accomplishments.  if you find area your boss has marked a NI, discuss it.  Ask him/her or suggest ways you can improve.  Show a desire to improve and leave with a positive attitude.  If you find the ni stems from a particular incident, think of ways you have implemented to improve the area, process, whatever the case may be, and bring this to your bosses attention.  

Lots of great advice here. in the posts.  Let us hear how you decided to handle this and how it turns out.