What do you mean by "Handle Nulls" There are several functions, like ZN, IFNULL, and ISNULL that relate to handling nulls. Perhaps a sample packaged workbook, along with what you expect as a result, would help us help you. Also, this thread did not get posted to the general "Forums" section of the site, so you may want to move it there for more visibility. This was a problem with the forum (threads not going where people expected), and they've made some changes so hopefully this won't occur for you in the future.
Tableau can work with NULLs, that is, they are a valid value. You can exclude them, filter them, even alias them.
Posting questions isn't a race so take your time and give us details, tell us exactly what you're looking to achive