public ByteSource getRaw(int fieldIdx) {
    PdxField ft = getPdxType().getPdxFieldByIndex(fieldIdx);
    if (ft == null) {
      throw new InternalGemFireException("unknown field " + fieldIdx);
    }
    return getRaw(ft);
  }
@param idx of the variable length field
@return the offset to the variable length field
geode-core/src/main/java/org/apache/geode/pdx/internal/PdxReaderImpl.java