public static function header($message, $header)
    {
        $match = self::headerLines($message, $header);
        return $match ? implode(', ', $match) : null;
    }
public static function header($message, $header)
    {
        $match = self::headerLines($message, $header);
        return $match ? implode(', ', $match) : null;
    }
public static function header ( $ message , $ header ) { $ match = self :: headerLines ( $ message , $ header ) ; return $ match ? implode ( ', ' , $ match ) : null ; }
Gets a header value from a message as a string or null

This method searches through the "headers" key of a message for a header
using a case-insensitive search. The lines of the header are imploded
using commas into a single string return value.

@param array  $message Request or response hash.
@param string $header  Header to retrieve

@return string|null Returns the header string if found, or null if not.
Gets a header value from a message as a string or null