Catch exception from callable

[juuuuuu]

As noticed in #260 there is an issue when trying to check if a JSON node is null or not.
I'll rather prefer to thow an exception here in order to avoid a "silent" return in a try/catch block.
The PropertyAccessor's getValue() method will throw an throwInvalidArgumentException exception in this case.

Description:
Given I have the following JSON to test, for example (any valid JSON will do the trick):

{
  "fieldA": "toto",
  "fieldB": "tata"
}

And I want to check that "notExistingField" should not be null.
The following step is a success: And the JSON node "notExistingField" should not be null.
I was doing TDD, and I expected my test to fail.

Before I add/update tests, let me know what do you think about it.
Thanks.