On 04/08/2015 09:42 AM, Mario Guerra wrote:
  Suppose this:
 update_domain guerra.cr NULL NULL NULL (NULL GUERRA-CR-K NULL)
 This example adds keyset GUERRA-CR-K to domain guerra.cr.
 Now lets try to dissociate that keyset:
 update_domain guerra.cr NULL NULL NULL (NULL () NULL)
 It does not work. Notice that I don't use NULL which, in that context
 does not touch the keyset entry. () should mean no keyset, right?. The
 same applies to dissociating an nsset making the domain a reserved
 one. For example:
 update_domain guerra.cr.NULL NULL NULL (() NULL NULL)
 Best regards. 
Answering my own question.
update_domain guerra.cr NULL NULL NULL ('' NULL NULL)