Unexpected @include behaviour with explicit null paramter

[SevInf]

We stumbled upon the following situation:

1. We have a query which declares Boolean variable with default value.
2. This variable is used as an argument for @include directive.
3. When executing query, variable is explictly set to null.

In this case, I'd expect to have an exception, as graphql-js does. Instead, any non-false value is treated as true.

Simplified example:

$queryType = new ObjectType([
    'name' => 'Query',
    'fields' => [
        'test' => [
            'type' => Type::string(),
        ]
    ]
]);

$schema = new Schema([
    'query' => $queryType
]);

$root = [
    'test' => '123'
];

$query = <<<GQL
    query Q(\$include: Boolean = false) {
        test @include(if: \$include)
    }
GQL;

$vars = [
    'include' => null,
];
$result = GraphQL::executeQuery($schema, $query, $root, null, $vars);
print_r($result->data);

This code prints:

Array
(
    [test] => 123
)

Where equivalent JS code throws:

 GraphQLError: Argument "if" of non-null type "Boolean!" must not be null.

[SevInf]

It looks like #262 resolves it

[vladar]

This is fixed in master via bf4e7d4