[miclf]

Just a quick fix of docblock tags that do not match actual code, thus causing static analysis tools to report errors.

There are 3 properties documented as non-nullable strings but that can be set to null in some cases: assetRoot, forcedRoot and forceScheme.

assetRoot can be set to null in the class constructor, because it defaults to null:

public function __construct(RouteCollectionInterface $routes, Request $request, $assetRoot = null)
{
    $this->routes = $routes;
    $this->assetRoot = $assetRoot;

    $this->setRequest($request);
}

forcedRoot can be set to null in forceRootUrl() (directly or via useOrigin()):

public function forceRootUrl($root)
{
    $this->forcedRoot = $root ? rtrim($root, '/') : null;

    $this->cachedRoot = null;
}

forceScheme, finally, can be set to null in the forceScheme() method:

public function forceScheme($scheme)
{
    $this->cachedScheme = null;

    $this->forceScheme = $scheme ? $scheme.'://' : null;
}