Returns a string, in character format, that represents hexstring converted to character. The returned string has half as many bytes as the original hexstring. hexstring can be of any length. If necessary, it is padded with a leading zero to make an even number of hexadecimal digits.
You can optionally include whitespace characters in hexstring (at byte boundaries only, not leading or trailing) to improve readability; they are ignored.
If hexstring is null, the function returns a null string.
