What are exceptions good for? Consider this window:
The lookup buttons are not really needed unless the user do not remember the code, and when the system is often used that rarely happen. Therefore, the window may look cleaner like this:
What window is nicer, is up to you. In any case, you have the choice. If you set up a small value for any of these entries, all the small buttons in your system may automatically skipped from processing, as you can see in the picture above.