code: public CustomFields updateCustomField(String accountId, String customFieldId, CustomField customField) throws ApiException {
      return updateCustomField(accountId, customFieldId, customField, null);
    }
docs: Updates an existing account custom field.
  
  @param accountId The external account number (int) or account ID Guid. (required)
  @param customFieldId  (required)
  @param customField  (optional)
  @return CustomFields