Composer installed 0.1.3, as the package version constraint was ~0.1.0.

This version can't correctly handle a property documented as mixed:

/**
 * The notification's source payload, data or message
 *
 * @var mixed
 */
public $rawContent;

With this version, JsonMapper raises the following issue:

Class '\Nasqueron\Notifications\Notifications\mixed' not found

This is a known bug, fixed upstream:
https://github.com/cweiske/jsonmapper/issues/33

The version is bumped to get this fix.

Run tests to ensure current mappings still work.

Test this code works:

private function getNotification () : Notification {
    $mapper = new \JsonMapper();
    return $mapper->map(
        json_decode($this->rawRequestContent),
        new Notification
    );
}