NaN Summarizing Units Without Rent Information

[ColinBuyck]

A listing in san jose had multiple units without the rent or rent as percentage income specified. This led to the experience captured down below. Further testing showed that a single unit without rent information was handled by showing n/a but multiple was leading to this confusing output. Ideally, the multiple units case should also display as n/a

QA: https://bloom.exygy.dev/ and https://partners.bloom.exygy.dev/sign-in
Add multiple units of the same unit type to a listing that have no rent or rent as a percentage of income information. Ensure that the unit summary displays with n/a rather than NaN per month.