docs: @Override
  	public String valueString(String headerValue)
  	{
  		// make sure the value is valid
  		for (int i = 0, count = headerValue.length(); i < count; ++i)
  		{
  			char c = headerValue.charAt(i);
  			if ((c < 0x20 || c > 0xff) && c != 0x09)
  			{
  				throw new IllegalArgumentException(String.format("String '%s' contains non-printable or non-ASCII characters, which is not allowed in headers",
  					headerValue));
  			}
  		}
  		return headerValue;
  	}