$data references pointing to an undefined object cause an exception

[jessepinho]

Similar to #57, but for $data references: When a JSON schema has a $data reference to a key on an object that's undefined, JJV throws TypeError: Cannot call method 'hasOwnProperty' of undefined.

It appears that JJV calls hasOwnProperty() on the undefined value (inside resolveObjectRef) before checking that the value is in fact an object, resulting in this error.

How to handle this is unfortunately not explicitly defined in the v5 $data proposal, but I just wanted to point out that this is unexpected behavior.

To reproduce, run coffee test.coffee:

# test.coffee
jjv = require "jjv"

validator = jjv()

validator.addSchema "testSchema",
  type: "object"
  properties:
    a:
      type: "integer"
      minimum:
        "$data": "/b/c"

validator.validate "testSchema", a: 1, b: undefined

Note that the exception is not thrown when b is missing (in the above example)—only when it is explicitly set to undefined.