public function setAdditionalUrlParam($key, $value)
	{
		// Get the old value to return and set the new one for the URL parameter.
		$result = isset($this->_additionalUrlParams[$key]) ? $this->_additionalUrlParams[$key] : null;

		// If the passed parameter value is null unset the parameter, otherwise set it to the given value.
		if ($value === null)
		{
			unset($this->_additionalUrlParams[$key]);
		}
		else
		{
			$this->_additionalUrlParams[$key] = $value;
		}

		return $this;
	}