==== tests/cases/compiler/operatorAddNullUndefined.ts (4 errors) ====
    enum E { x }
    var x1 = null + null;
             ~~~~~~~~~~~
!!! Operator '+' cannot be applied to types 'null' and 'null'.
    var x2 = null + undefined;
             ~~~~~~~~~~~~~~~~
!!! Operator '+' cannot be applied to types 'undefined' and 'undefined'.
    var x3 = undefined + null;
             ~~~~~~~~~~~~~~~~
!!! Operator '+' cannot be applied to types 'null' and 'null'.
    var x4 = undefined + undefined;
             ~~~~~~~~~~~~~~~~~~~~~
!!! Operator '+' cannot be applied to types 'undefined' and 'undefined'.
    var x5 = 1 + null;
    var x6 = 1 + undefined;
    var x7 = null + 1;
    var x8 = undefined + 1;
    var x9 = "test" + null;
    var x10 = "test" + undefined;
    var x11 = null + "test";
    var x12 = undefined + "test";
    var x13 = null + E.x
    var x14 = undefined + E.x
    var x15 = E.x + null
    var x16 = E.x + undefined