cdm/src/main/java/ucar/nc2/dataset/StructureDS.java
@Override
  public Array reallyRead(Variable client, Section section, CancelTask cancelTask) throws IOException, InvalidRangeException {
    if (section.computeSize() == getSize())
      return _read();

    Array result;
    if (hasCachedData())
      result = super.reallyRead(client, section, cancelTask);
    else if (orgVar != null)
      result = orgVar.read(section);
    else {
      throw new IllegalStateException("StructureDS has no way to get data");
      //Object data = smProxy.getFillValue(getDataType());
      //return Array.factoryConstant(dataType.getPrimitiveClassType(), section.getShape(), data);
    }

    // do any needed conversions (enum/scale/offset/missing/unsigned, etc)
    return convert(result, section);
  }
@Override
  public Array reallyRead(Variable client, Section section, CancelTask cancelTask) throws IOException, InvalidRangeException {
    if (section.computeSize() == getSize())
      return _read();

    Array result;
    if (hasCachedData())
      result = super.reallyRead(client, section, cancelTask);
    else if (orgVar != null)
      result = orgVar.read(section);
    else {
      throw new IllegalStateException("StructureDS has no way to get data");
      //Object data = smProxy.getFillValue(getDataType());
      //return Array.factoryConstant(dataType.getPrimitiveClassType(), section.getShape(), data);
    }

    // do any needed conversions (enum/scale/offset/missing/unsigned, etc)
    return convert(result, section);
  }
section of regular Variable