Why empty adjustment layer with blend mode multiply darken images?

Question

I know blend mode "Multiply" means multiplying the colour (0 to 255) of its layer, with the visible underneath (0 to 255), then divided by 255, forms the resulting colour (0 to 255).

As a visual effect, it is always darkened.

However, adding an empty adjustment (level or curve) layer, with NO adjustment content in it. Using blend mode multiply also darkens the image. Why?

Its effect is NOT like blending a white layer, nor blending a 50% grey layer.

An empty adjustment layer is regarded as transparent, somehow. But what explains the darken effect while blending with multiply?

Answer 1

I found out the answer by testing.

Blending with an empty adjustment layer is exactly the same as blending with itself duplication.

So the result of Multiply is, colour of itself (0 to 255) * colour of itself (0 to 255) / 255.