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'use strict';
const isDefiningProjection = require('./isDefiningProjection');
/*! * ignore */
module.exports = function isExclusive(projection) {  if (projection == null) {    return null;  }
  const keys = Object.keys(projection);  let ki = keys.length;  let exclude = null;
  if (ki === 1 && keys[0] === '_id') {    exclude = !projection._id;  } else {    while (ki--) {      // Does this projection explicitly define inclusion/exclusion?      // Explicitly avoid `$meta` and `$slice`      const key = keys[ki];      if (key !== '_id' && isDefiningProjection(projection[key])) {        exclude = (projection[key] != null && typeof projection[key] === 'object') ?          isExclusive(projection[key]) :          !projection[key];        break;      }    }  }
  return exclude;};