code: public static byte[] toByteArray(CharSequence hexString) {
          if (hexString == null) {
              return null;
          }
          return toByteArray(hexString, 0, hexString.length());
      }
docs: Creates a byte array from a CharSequence (String, StringBuilder, etc.)
  containing only valid hexidecimal formatted characters.
  Each grouping of 2 characters represent a byte in "Big Endian" format.
  The hex CharSequence must be an even length of characters. For example, a String
  of "1234" would return the byte array { 0x12, 0x34 }.
  @param hexString The String, StringBuilder, etc. that contains the
  sequence of hexidecimal character values.
  @return A new byte array representing the sequence of bytes created from
  the sequence of hexidecimal characters.  If the hexString is null,
  then this method will return null.