Returns a string, in character format, that represents the receiving
string, which is a hexadecimal string converted to character. The returned string
is half as many bytes as the receiving string. The receiving string can be
any length. If necessary, it is padded with a leading 0 to make an even number
of hexadecimal digits.
You can optionally include whitespace in the receiving string (at byte
boundaries only, not leading or trailing) to improve readability; they are
ignored.
If the receiving string is null, the method returns a null string.
