docs: function hasNext(cursor, callback) {
    const Cursor = require('../cursor');
  
    if (cursor.s.currentDoc) {
      return callback(null, true);
    }
  
    if (cursor.isNotified()) {
      return callback(null, false);
    }
  
    nextObject(cursor, (err, doc) => {
      if (err) return callback(err, null);
      if (cursor.s.state === Cursor.CLOSED || cursor.isDead()) return callback(null, false);
      if (!doc) return callback(null, false);
      cursor.s.currentDoc = doc;
      callback(null, true);
    });
  }