UglifyJS/test/compress/issue-2871.js

comparison_with_undefined: {
    options = {
        comparisons: true,
    }
    input: {
        a == undefined
        a != undefined
        a === undefined
        a !== undefined

        undefined == a
        undefined != a
        undefined === a
        undefined !== a

        void 0 == a
        void 0 != a
        void 0 === a
        void 0 !== a
    }
    expect: {
        null == a
        null != a
        void 0 === a
        void 0 !== a

        null == a
        null != a
        void 0 === a
        void 0 !== a

        null == a
        null != a
        void 0 === a
        void 0 !== a
    }
}