text: CREATE TABLE issue_104 (
    id serial8 not null primary key,
    groupid bigint,
    field text
  );
  CREATE INDEX idxissue104 ON issue_104 USING zombodb (zdb('issue_104', ctid), zdb(issue_104)) WITH (url='http://localhost:9200/');
  
  INSERT INTO issue_104 (groupid, field) VALUES (1, 'foo');
  INSERT INTO issue_104 (groupid, field) VALUES (1, 'bar');
  INSERT INTO issue_104 (groupid, field) VALUES (1, 'dog');
  INSERT INTO issue_104 (groupid, field) VALUES (1, 'cat');
  
  SELECT assert(count(*), 0, 'found nothing') FROM issue_104 WHERE zdb('issue_104', ctid) ==> '#expand<groupid=<this.index>groupid>(field:null)';
  
  UPDATE issue_104 SET field = NULL WHERE field = 'foo';
  SELECT assert(count(*), 4, 'found everything') FROM issue_104 WHERE zdb('issue_104', ctid) ==> '#expand<groupid=<this.index>groupid>(field:null)';
  
  UPDATE issue_104 SET field = 'foo' WHERE field IS NULL;
  SELECT assert(count(*), 0, 'found nothing') FROM issue_104 WHERE zdb('issue_104', ctid) ==> '#expand<groupid=<this.index>groupid>(field:null)';
  
  DROP TABLE issue_104;