code: public String encodeStringAsBase64(String value) throws ConversionException {
          try {
              return encodeStringAsBase64Internal(value);
          } catch (IOException e) {
              // Will never happen
              return null;
          }
      }
docs: Encode a String in base64. The content of the string is first encoded
  as UTF-8 bytes, the bytes are then base64 encoded. The resulting base64
  value is returned as a String.
  
  @param value The String to encode
  @return The encoded base64 String
  @throws ConversionException If the String content can not be UTF-8 encoded.