Repository.php __call returns throw when no nodes are found!

[cedriclevarlet]

As the title says the current implementation of the __call method throws the following:

new InvalidArgumentException('Method name must begin with "findBy" or "findOneBy"!');

This happens whenever a findBy or findOneBy is called and no node is found. Whilst this could be intended I do not think this is intuitive and is in fact quite misleading.

I have replaced this implementation the following lines as it seems to be more logical.

} else {
throw new InvalidArgumentException('Method name must begin with "findBy" or "findOneBy"!');
}
return null;

[lphuberdeau]

Please submit a pull request request.