De-serialization errors if using definitions-like object

[edgarmueller]

e.g.

{
  "foo": {
    "a": {"type": "string" },
    "b": {"type": "string" }
  }
}

causes the Reads to fail.

[edgarmueller]

My mistake, there was a typo in a type field, I will create follow-up issues to improve readability of deserialization errors.