mongoose: Getter gets called with undefined parameter

getter.coffee

mongoose = require 'mongoose'

TestSchema = new mongoose.Schema {
  number:
    type: Number
    set: (x) -> return x/2 
    get: (x) ->
      console.log 'getter called with undefined' if not x?
      x*2 if x?
}

Test = mongoose.model 'test', TestSchema
test = new Test {number: 42.42}
console.log test.number