" unless there is a State law which says otherwise"
You want to move the goalposts. This was about whether or not the phase "this note is legal tender for all debts public and private" meant that the gas station attendent MUST accept your fifty or the gas is free. The presence or absence of a state law won't change the fact that that phrase mandates only the Federal Reserve to accept it. But, I'll play anyway. Is there such a law in your state? Can you quote the statute please?