If you do not submit a previously set optional parameter with the same data, it will be overwritten with null, e.g. if a value is set for "addr2" and you do not resubmit the same value during the update, the value for "addr2" will be set to null
Therefore, we recommend to get the contemporary account information (see Get Account Information) and reuse this data apart from the changed fields.
For more information on handling null values and empty strings in requests, please check our FAQ section on "Sending parameter with null value".