fromJson method doesn't throw an appropriate exception for invalid JSON

[becw]

When invalid JSON is passed to ApiProblem::fromJson(), I get a PHP notice and an exception:

• Argument 1 passed to Crell\ApiProblem\ApiProblem::decompile() must be an array, null given
• The provided problem string is invalid. The "title" property is required.

I think it would be appropriate to throw an exception about the invalid JSON, rather than one about the missing title.

[Crell]

Hm, I would agree. How do we detect invalid JSON, though? Please file a PR. :-)

[Crell]

We should probably do the same for unparsable XML, too.

[xait-arne-trodahl]

Some clues can be found in the examples here http://php.net/manual/en/function.json-last-error.php

[simensen]

For JSON you can consider using seld/jsonlint as that can check to make sure that the JSON is well-formed. It does not help the XML problem.

https://packagist.org/packages/seld/jsonlint

[Crell]

JSON has been resolved here: #14