N302 in X12 834: A Field Guide to Address Information
The field nobody tests until a member complains their ID card went to the building, not the unit.
N302 is an optional second address line, used when a member's mailing address needs more than N301 alone can hold — an apartment number, suite, unit, or floor designation. It's free-form text like N301, and it's simply absent when a member's address fits on one line.
What this field needs to handle
Example
A synthetic N3 where N302=APT 4B supplements the street line in N301 with a unit number for a multi-unit building.
Where this trips people up
Test data generators often either always populate N302 or never populate it, and both extremes hide real bugs. Always populating it never tests whether the parser correctly treats a single-line address as complete rather than expecting a second segment element that isn't there. Never populating it means a mailing vendor's template that assumes a second line might exist never gets exercised, and the first real member with an apartment number gets a piece of mail routed to the wrong door. Mix both cases in your synthetic member population so the presence or absence of N302 is actually variable, the way it is in a real file.