Make null falsey.

test/logical_operator/and.wren

@@ -0,0 +1,20 @@
+// Note: These tests implicitly depend on ints being truthy.
+//       Also rely on IO.print() returning its argument.
+
+// Return the first non-true argument.
+IO.print(false && 1) // expect: false
+IO.print(true && 1) // expect: 1
+IO.print(1 && 2 && false) // expect: false
+
+// Return the last argument if all are true.
+IO.print(1 && true) // expect: true
+IO.print(1 && 2 && 3) // expect: 3
+
+// Short-circuit at the first false argument.
+IO.print(true) && // expect: true
+    IO.print(false) && // expect: false
+    IO.print(false) // should not print
+
+// Swallow a trailing newline.
+IO.print(true &&
+    true) // expect: true