If, as Phil has assumed/you've implied, you are exporting data from multiple source columns and concatenating them into a single export/destination column, you still need to account for the NULL fields in that concatenated string. Whether your final "export column" is in a fixed-width, or otherwise delimited format, you'd still want to pad those NULLed fields with some acceptable value (spaces, in a fixed-width file, for example). If you don't account for those NULL values/fields, then your export format/layout will definitely be "off."

If this is not what you're after, please detail your situation further.