public function negotiateRdfContentType($acceptHeader)
 {
     $contentTypes = array('application/rdf+xml', 'text/turtle', 'application/ld+json');
     $negotiationResults = array();
     $negotiatedType = http_negotiate_content_type($contentTypes, $negotiationResults);
     if (!empty($negotiationResults)) {
         return RdfType::getByMimeType($negotiatedType);
     }
     return null;
 }
 public function testGetByMimeTypeUnknown()
 {
     $this->assertNull(RdfType::getByMimeType('text/html'));
 }