When updating a resource, the Resources API uses PATCH endpoints and field masks. A PATCH endpoint means that only the fields specified in the request will be updated. Alternatively, a field mask explicitly lists the fields to update, regardless of which fields are specified in the request. You must use a field mask if you want to clear the value from a field.
The example below uses a field mask.
phone
field is updatedemail
field is cleared.name
field is not updated as it is not included in the field mask.