src/Riak/HeadersTrait.php
protected function getHeader($key)
    {
        return isset($this->headers[$key]) ? $this->headers[$key] : NULL;
    }
protected function getHeader($key)
    {
        return isset($this->headers[$key]) ? $this->headers[$key] : NULL;
    }
Retrieve the value for a header, null if not set

@param $key

@return string|null