comparator with null values

We have some code which sorts a list of addresses based on the distance between their coordinates. this is done through collections.sort with a custom comparator. However from time to time an address without coordinates is in the list causing a NullPointerException. My initial idea to fix this was to have the comparator return 0 as distance for addresses where at least one of the coordinates is null. I fear this might lead to corruption of the order the 'valid' elements in the list. so is returning a '0' values for null data in a comparator ok, or is there a cleaner way to resolve this?