Troubleshooting HubSpot API: Updating Empty Contact Fields

HubSpot integration question. When you lookup an object in HubSpot you get a list of its properties returned. The issue I'm having is properties that exist in HubSpot but have no value don't get returned. No key. So, for instance, if I wanted to update a contact's city (via the City property) it doesn't get returned. A properties name in the UI is different than in the API. First Name vs firstname. So, I'm struggling to know the name of properties to update. My reason for doing this is that I don't want to update certain fields where the CRM may be more accurate than me.