Error with unique index

[edsadr]

if you have sotheing like this in a model:

username: {
    type: String,
    required: true,
    index: {
      unique: true
    }
  }

You will get an error while adding a duplicate:

/home/edsadr/Sites/lotto/admin/node_modules/mongoose/lib/utils.js:413
        throw err;
              ^
TypeError: Cannot set property 'error' of undefined
  at Promise.<anonymous> (/home/edsadr/Sites/lotto/admin/node_modules/penguin/src/index.coffee:451:9)
  at Promise.<anonymous> (/home/edsadr/Sites/lotto/admin/node_modules/mongoose/node_modules/mpromise/lib/promise.js:172:8)
  at emitOne (events.js:77:13)
  at Promise.emit (events.js:166:7)
  at Promise.emit (/home/edsadr/Sites/lotto/admin/node_modules/mongoose/node_modules/mpromise/lib/promise.js:84:38)
  at Promise.reject (/home/edsadr/Sites/lotto/admin/node_modules/mongoose/node_modules/mpromise/lib/promise.js:111:15)
  at Promise.error (/home/edsadr/Sites/lotto/admin/node_modules/mongoose/lib/promise.js:95:15)
  at handleSave (/home/edsadr/Sites/lotto/admin/node_modules/mongoose/lib/model.js:95:15)
  at /home/edsadr/Sites/lotto/admin/node_modules/mongoose/lib/utils.js:408:16
  at /home/edsadr/Sites/lotto/admin/node_modules/mongoose/node_modules/mongodb/lib/mongodb/collection/core.js:123:18
  at /home/edsadr/Sites/lotto/admin/node_modules/mongoose/node_modules/mongodb/lib/mongodb/db.js:1195:7
  at /home/edsadr/Sites/lotto/admin/node_modules/mongoose/node_modules/mongodb/lib/mongodb/db.js:1903:9
  at Server.Base._callHandler (/home/edsadr/Sites/lotto/admin/node_modules/mongoose/node_modules/mongodb/lib/mongodb/connection/base.js:453:41)
  at /home/edsadr/Sites/lotto/admin/node_modules/mongoose/node_modules/mongodb/lib/mongodb/connection/server.js:487:18
  at [object Object].MongoReply.parseBody (/home/edsadr/Sites/lotto/admin/node_modules/mongoose/node_modules/mongodb/lib/mongodb/responses/mongo_reply.js:68:5)
  at [object Object].<anonymous> (/home/edsadr/Sites/lotto/admin/node_modules/mongoose/node_modules/mongodb/lib/mongodb/connection/server.js:445:20)
  at emitOne (events.js:77:13)
  at [object Object].emit (events.js:166:7)
  at [object Object].<anonymous> (/home/edsadr/Sites/lotto/admin/node_modules/mongoose/node_modules/mongodb/lib/mongodb/connection/connection_pool.js:207:13)
  at emitTwo (events.js:87:13)
  at [object Object].emit (events.js:169:7)
  at Socket.<anonymous> (/home/edsadr/Sites/lotto/admin/node_modules/mongoose/node_modules/mongodb/lib/mongodb/connection/connection.js:440:22)
  at emitOne (events.js:77:13)
  at Socket.emit (events.js:166:7)
  at readableAddChunk (_stream_readable.js:146:16)
  at Socket.Readable.push (_stream_readable.js:109:10)
  at TCP.onread (net.js:517:20)