Shader Graph Lerp Node causes failing output

Hello,
I don’t know what is wrong with the shader. See image. As soon as I insert a Lerp Node and connect it to the output, the output gets blank. What am I foing wrong. I simply want to have a color gradient along Y for a sprite.
I am using Unity 2019.3.7f1, Shader Graph 7.1.8, URP 7.1.8.

Also the node right before the master is exactly what I want.

Hope someone can help, thank you!

Does someone facing the same issues?

Input colors were transparent…