anchor.diff:        this.jobTitle,
         this.middleName,
         this.prefix,
  -      this.suffix
  +      this.suffix,
  +      this.birthday,
       ].where((s) => s != null));
     }
   }
  
positive.code:               .toSet()
                .union(other.postalAddresses?.toSet() ?? Set())
                .toList(),
        avatar: this.avatar ?? other.avatar);
  
    /// Returns true if all items in this contact are identical.
    @override
  
negative.code: }
  
  class Contact {
    Contact({
      this.givenName,
      this.middleName,
      this.prefix,
      this.suffix,
      this.familyName,
      this.company,
      this.jobTitle,
      this.emails,
      this.phones,
      this.postalAddresses,
      this.avatar,
      this.birthday,
    });
  
    String identifier, displayName, givenName, middleName, prefix, suffix, familyName, company, jobTitle;
    Iterable<Item> emails = [];
    Iterable<Item> phones = [];
    Iterable<PostalAddress> postalAddresses = [];
    Uint8List avatar;
    DateTime birthday;
  
    String initials() {
      return ((this.givenName?.isNotEmpty == true ? this.givenName[0] : "") +
  