Given the task definition and input, reply with output. Given a travel related situation, and given a specific question about the situation, summarize the question into a title

Arrival cards, Immigration cards, Custom declaration cards at airports often have a field that asks for home address/country of residence, etc...

What if a backpacker no longer maintains a residence and therefore has no home address (and has no family that has a home address either)? How should a backpacker fill out that field? Should he leave it blank? Can he write a non-residential mailing address instead? Do immigration/custom officers even care about that field?
How should a backpacker fill out home address field in immigration/custom cards