Can't be sure: we don't know (for instance) what $user_input contains, and making assumptions about that wouldn't help you solve this.

Do you mean by "I am not getting the desired o/p. I am handling end_date text box empty case" that you are getting the output you want for the empty case but not for the other one, or that the empty case isn't being handled right? I assume you mean the second ... but I still can't tell from what you've posted where the problem is. Need more context.

What is the smallest piece of code that runs and exhibits the aberrant behavior? (By the way, once you have that, you have a test for this bug, and the start of a test suite!)