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// Setting a Map key to undefined, or a missing argument, isn't the same as deleting it.
var m = new Map;
m.set(42, undefined);
assertEq(m.has(42), true);
assertEq(m.get(42), undefined);
m.set(42, "wrong");
m.set(42);
assertEq(m.has(42), true);
assertEq(m.get(42), undefined);
m.set();
assertEq(m.has(undefined), true);
assertEq(m.get(undefined), undefined);