net0 in nmPEX

Hello again! I made a block with 4 pins: VDD, GND, in, out

When I run nmPEX and I read the netlist, I see it finds capacitances between GND and net0! What is net0? How should I have to interpret it? Let's say I have a capacitance between out and GND, and another one between out and net0: should I have to add those capacitance (thus considering net0=GND)? What about the capacitance between GND and net0, then?

Thanks for your help!