Check for `None` key fails when using `parse`

[silentninja]

Issue Description

When using simdjson.Parser.parse, checking if a None key exists in the parsed object results in a TypeError: expected bytes, NoneType found.

Example Code:

import simdjson
parser = simdjson.Parser()
doc = parser.parse(b'{"res": [{"name": "first"}, {"name": "second"}]}')
if not None in doc:  # This line raises the error
    pass

Error:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "simdjson/csimdjson.pyx", line 316, in csimdjson.Object.__contains__
TypeError: expected bytes, NoneType found

---

Expected Behavior

The check should return False (as it does with simdjson.loads), since None is not a valid JSON key.

Working Example with simdjson.loads:

import simdjson
doc = simdjson.loads(b'{"res": [{"name": "first"}, {"name": "second"}]}')
if not None in doc:  # Correctly returns False
    pass