code: PatchEntry getEntry(final String name, boolean addOn) {
          return addOn ? addOns.get(name) : layers.get(name);
      }
docs: Get a patch entry for either a layer or add-on.
  
  @param name  the layer name
  @param addOn whether the target is an add-on
  @return the patch entry, {@code null} if it there is no such layer