public function serializeNull(XmlStreamWriter $xmlWriter, string $tagName = null): XmlStreamWriter
    {
        return $xmlWriter->writeStartElement(null === $tagName ? 'null' : $tagName)
                ->writeElement('null')
                ->writeEndElement();
    }
public function serializeNull(XmlStreamWriter $xmlWriter, string $tagName = null): XmlStreamWriter
    {
        return $xmlWriter->writeStartElement(null === $tagName ? 'null' : $tagName)
                ->writeElement('null')
                ->writeEndElement();
    }
public function serializeNull ( XmlStreamWriter $ xmlWriter , string $ tagName = null ) : XmlStreamWriter { return $ xmlWriter -> writeStartElement ( null === $ tagName ? 'null' : $ tagName ) -> writeElement ( 'null' ) -> writeEndElement ( ) ; }
serializes null to xml

@param   \stubbles\xml\XmlStreamWriter  $xmlWriter  xml writer to write serialized value into
@param   string                         $tagName    name of the surrounding xml tag
@return  \stubbles\xml\XmlStreamWriter
@since   1.6.0
serializes null to xml