if (d == null) {
// No: only evaluation results are returned, no error messages
// v = leaf.getScale().createValue();
// v.setComment("ImageMagick comparison failed");
} else {
v = scale.createValue();
if (v instanceof FloatValue) {
((FloatValue)v).setValue(d);
v.setComment("computed by ImageMagick compare");
} else if (v instanceof PositiveFloatValue) {
((PositiveFloatValue)v).setValue(d);