title: Mongoose TypeError when creating a schema that used Number
body: <p>I've got a schema that uses numbers as follows.</p>
  
  <pre><code>var mongoose = require('mongoose')
      , Schema = mongoose.Schema
      , ObjectId = Schema.Types.ObjectId
      , Mixed = Schema.Types.Mixed
      , Number = Schema.Types.Number
      , Date = Schema.Types.Date
  
  var ItemSchema = new Schema({
      quantity:{type:Number, required:true, min:1},
      category:{type:String, required:true, enum:categoryList},
      description:{type:String, required:true},
      cost:{type:Number, required:true, min:0, default:0},
      appraisedValue:{type:Number, min:0, default:0},
      appraisedOn:Date,
      purchasedOn:Date,
      purchasedFrom:String,
      brand:String,
      dynamicFieldList:[DynamicFieldSchema]
  })
  exports.ItemSchema = ItemSchema
  exports.Item = mongoose.model('Item', ItemSchema)
  </code></pre>
  
  <p>But when I attempt to run my application, I receieve a TypeError: Undefined type at 'quantity'.  This also occurs at 'cost', if the quantity value is commented out.</p>
  
  <p>The stack trace is:</p>
  
  <pre><code>C:\Users\a\Documents\Git\has-inventory.js\node_modules\mongoose\lib\schema.js:325
  throw new TypeError('Undefined type at `' + path +
  
  TypeError: Undefined type at `quantity`
    Did you try nesting Schemas? You can only nest using refs or arrays.
  at Function.Schema.interpretAsType (C:\Users\a\Documents\Git\has-inventory.js\node_modules\mongoose\lib\schema.js:325:11)
  at Schema.path (C:\Users\a\Documents\Git\has-inventory.js\node_modules\mongoose\lib\schema.js:268:29)
  at Schema.add (C:\Users\a\Documents\Git\has-inventory.js\node_modules\mongoose\lib\schema.js:200:12)
  at new Schema (C:\Users\a\Documents\Git\has-inventory.js\node_modules\mongoose\lib\schema.js:69:10)
  at Object.&lt;anonymous&gt; (C:\Users\a\Documents\Git\has-inventory.js\domain\inventory.js:34:18)
  at Module._compile (module.js:449:26)
  at Object.Module._extensions..js (module.js:467:10)
  at Module.load (module.js:356:32)
  at Function.Module._load (module.js:312:12)
  at Module.require (module.js:362:17)
  </code></pre>