Change Mongo.setReadPref(mode, tagSet) to Mongo.setReadPref(mode, tagSet, hedgeOptions) and Cursor.readPref(mode, tagSet) to cursor.readPref(mode, tagSet, hedgeOptions), where hedgeOptions is an optional argument of the form {enabled: <bool>}.
Similar to the $readPreference subkey {hedge: {enabled: <bool>}}, passing {} is equivalent to passing
{enabled: true}since 'enabled' defaults to true.