title: MongoExpress shows "Cannot read property 'listDatabases' of undefined" error
body: <p>I tried to create Mongo and Mongo-Express server using <strong>docker-compose.yml</strong>. Here's my setting</p>
  
  <pre><code>version: "3"
  services:
    mongo:
      image: "mongo:3-stretch"
      environment:
        - MONGO_INITDB_ROOT_USERNAME=devroot
        - MONGO_INITDB_ROOT_PASSWORD=devroot
        - MONGO_INITDB_DATABASE=DataBank
      ports:
         - "27017:27017"
    mongo-express:
      image: "mongo-express:latest"
      environment:
        - ME_CONFIG_MONGODB_SERVER=mongo
        - ME_CONFIG_MONGODB_PORT=27017
        - ME_CONFIG_MONGODB_ENABLE_ADMIN=false
        - ME_CONFIG_MONGODB_AUTH_DATABASE=admin
        - ME_CONFIG_MONGODB_AUTH_USERNAME=devroot
        - ME_CONFIG_MONGODB_AUTH_PASSWORD=devroot
        - ME_CONFIG_OPTIONS_EDITORTHEME=ambiance
        - ME_CONFIG_BASICAUTH_USERNAME=dev
        - ME_CONFIG_BASICAUTH_PASSWORD=dev
      depends_on:
        - mongo
      ports:
        - "8081:8081"
  </code></pre>
  
  <p>Results (There's an error here):</p>
  
  <pre><code>mongo-express_1  | Thu Feb  6 03:11:36 UTC 2020 retrying to connect to mongo:27017 (3/5)
  mongo-express_1  | /docker-entrypoint.sh: connect: Connection refused
  mongo-express_1  | /docker-entrypoint.sh: line 14: /dev/tcp/mongo/27017: Connection refused
  </code></pre>
  
  <p><br>
  Despite the first error, I still was able to access <a href="http://localhost:8081/" rel="nofollow noreferrer">http://localhost:8081/</a> But when logged-in successfully, it shows (another error):</p>
  
  <pre><code>mongo-express_1  | Database connected
  mongo-express_1  | Connecting to admin...
  mongo_1          | 2020-02-06T03:11:39.826+0000 I ACCESS   [conn2] Successfully authenticated as principal devroot on admin
  mongo-express_1  | Database admin connected
  mongo-express_1  | Admin database is not accessible
  mongo-express_1  | TypeError: Cannot read property 'listDatabases' of undefined
  mongo-express_1  |     at Object.connectionData.updateDatabases (/node_modules/mongo-express/lib/db.js:41:11)
  mongo-express_1  |     at /node_modules/mongo-express/lib/router.js:94:11
  mongo-express_1  |     at Layer.handle [as handle_request] (/node_modules/express/lib/router/layer.js:95:5)
  mongo-express_1  |     at next (/node_modules/express/lib/router/route.js:137:13)
  mongo-express_1  |     at Route.dispatch (/node_modules/express/lib/router/route.js:112:3)
  mongo-express_1  |     at Layer.handle [as handle_request] (/node_modules/express/lib/router/layer.js:95:5)
  mongo-express_1  |     at /node_modules/express/lib/router/index.js:281:22
  mongo-express_1  |     at param (/node_modules/express/lib/router/index.js:354:14)
  mongo-express_1  |     at param (/node_modules/express/lib/router/index.js:365:14)
  mongo-express_1  |     at Function.process_params (/node_modules/express/lib/router/index.js:410:3)
  mongo-express_1  | GET / 500 12.737 ms - 1049
  </code></pre>
  
  <p><br>
  What should I look in to?</p>