ImageDifferToPng#complementMaterialAsImage() is questionable

[kazurayam]

com.kazurayam.materialstore.base.reduce.differ.ImageDifferToPNG has the lines:

@Override
    public MaterialProduct stuffDiff(MaterialProduct mProduct) throws MaterialstoreException {
        ...
        Material left = complementMaterialAsImage(store, mProduct, mProduct.getLeft());
        BufferedImage leftImage = readImage(left.toPath());
        ...

v0.16.0, the complementMaterialAsImage() returns an instance of Material.

But now I think that this method should rather return an instance of Buffered Image. So that I can rewrite the above section as

@Override
    public MaterialProduct stuffDiff(MaterialProduct mProduct) throws MaterialstoreException {
        ...
        BufferedImage leftImage = complementMaterialAsImage(store, mProduct, mProduct.getLeft());
        ...

[kazurayam]

This idea was pointless.