TYPO3.Flow

The Uri::__construct() method basically relies on the parse_url() method. As of PHP documentation, http://de3.php.net/manual/en/function.parse-url.php, Changelog,

5.3.3 Removed the E_WARNING that was emitted when URL parsing failed.

So the constructor's code can, dependent of the PHP version in use, either throw a Warning exception or silently do nothing but let the Uri object be created since there is no other check:

 1    public function __construct($uriString) {
 2        if (!is_string($uriString)) throw new \InvalidArgumentException('The URI must be a valid string.', 1176550571);
 3
 4        $uriParts = parse_url($uriString);
 5        if (is_array($uriParts)) {
 6            $this->scheme = isset($uriParts['scheme']) ? $uriParts['scheme'] : NULL;
 7            $this->username = isset($uriParts['user']) ? $uriParts['user'] : NULL;
 8            $this->password = isset($uriParts['pass']) ? $uriParts['pass'] : NULL;
 9            $this->host = isset($uriParts['host']) ? $uriParts['host'] : NULL;
10            $this->port = isset($uriParts['port']) ? $uriParts['port'] : NULL;
11            $this->path = isset($uriParts['path']) ? $uriParts['path'] : NULL;
12            if (isset($uriParts['query'])) {
13                $this->setQuery ($uriParts['query']);
14            }
15            $this->fragment = isset($uriParts['fragment']) ? $uriParts['fragment'] : NULL;
16        }
17    }

I recommend to catch the Warning, if any, and throw an exception if parse_url returned FALSE (or is not an array, i.e. the else-block of the if().