true <= null; // expect runtime error
true <= true; // expect runtime error
true <= "s"; // expect runtime error
true <= 123; // expect runtime error

null <= null; // expect runtime error
null <= true; // expect runtime error
null <= "s"; // expect runtime error
null <= 123; // expect runtime error

123 <= null; // expect runtime error
123 <= true; // expect runtime error
123 <= "s"; // expect runtime error

"s" <= null; // expect runtime error
"s" <= true; // expect runtime error
"s" <= 123; // expect runtime error