Changes only the fields sent (BF-7493): JSON Merge Patch.

Send any updatable field, with the names PUT uses; fields not sent are left as they are. A key with null clears that field, except the eight PUT requires, which cannot be null. Keys match in any case. A key that is not an updatable field is a 400, and so is isActive: activate or deactivate a contractor in Bilflo. A value of the wrong JSON type is a 400 naming the key (numbers must be JSON numbers, dates yyyy-MM-dd). An empty body is a 400. A contractorId in the body must equal the route. customFields changes only the fields listed; an empty customFieldItemName clears one. Rules such as zip code, phone or SSN format apply only to values that change. dateOfBirth must be a calendar date yyyy-MM-dd; a changed value with a time zone (Z or an offset) is a 400. Error messages never repeat personal values, except that custom-field errors name the custom field and list item.