code: function Admin(db, topology, promiseLibrary) {
    if (!(this instanceof Admin)) return new Admin(db, topology);
  
    // Internal state
    this.s = {
      db: db,
      topology: topology,
      promiseLibrary: promiseLibrary
    };
  }
docs: @fileOverview The **Admin** class is an internal class that allows convenient access to
  the admin functionality and commands for MongoDB.
  
  **ADMIN Cannot directly be instantiated**
  @example
  const MongoClient = require('mongodb').MongoClient;
  const test = require('assert');
  // Connection url
  const url = 'mongodb://localhost:27017';
  // Database Name
  const dbName = 'test';
  
  // Connect using MongoClient
  MongoClient.connect(url, function(err, client) {
  // Use the admin database for the operation
  const adminDb = client.db(dbName).admin();
  
  // List all the available databases
  adminDb.listDatabases(function(err, dbs) {
  test.equal(null, err);
  test.ok(dbs.databases.length > 0);
  client.close();
  });
  });
   
  Create a new Admin instance (INTERNAL TYPE, do not instantiate directly)
  @class
  @return {Admin} a collection instance.