When using the ProductSubsetBuilder within an Operator, it's useful to optionally have the ProductSubset build treat virtual bands as real bands so that target products have real bands without any dependencies to bands that may not exist anymore.

In addBandsToProduct()

                boolean treatVirtualBandsAsRealBands = false;
                if(getSubsetDef() != null && getSubsetDef().treatVirtualBandsAsRealBands())
                    treatVirtualBandsAsRealBands = true;

                //@todo 1 se/se - extract copy of a band or virtual band to create deep clone of band and virtual band
                if (!treatVirtualBandsAsRealBands && sourceBand instanceof VirtualBand) {
                    VirtualBand virtualSource = (VirtualBand) sourceBand;
                    VirtualBand virtualBand = new VirtualBand(bandName,
                                                              sourceBand.getDataType(),
                                                              getSceneRasterWidth(),
                                                              getSceneRasterHeight(),
                                                              virtualSource.getExpression());
                    virtualBand.setCheckInvalids(virtualSource.getCheckInvalids());
                    destBand = virtualBand;
                } else {
                    destBand = new Band(bandName,
                                        sourceBand.getDataType(),
                                        getSceneRasterWidth(),
                                        getSceneRasterHeight());
                }