Cannot parse yexte:initial-value "::" for ipv6 address

leaf ipv6Address {
  description "Eight fields, separated by colons. Each field consists of up to four hexadecimal characters. Value of each field is in range 0-FFFF. Leading zeroes can be omitted in a field, and multiple groups of 16 bits of zeroes can be compressed to :: The :: can appear only once in an address.";
  type inet:ipv6-address-no-zone;
  yexte:initial-value "::";
}