must.throw returns unexpected `actual` value when testing message

[dzek69]

Consider this code:

const test = () => {
    throw new Error("Hi there");
};
describe("module", () => {
    it("throws correct error", () => {
        test.must.throw(Error, "Hello world");
    });
});

My IDE (PHPStorm 2017.1) can't diff expected and actual values for this, printing:

AssertionError: function test() {
    throw new Error("Hi there");
} must throw "Hello world"
Expected :"Hello world"
Actual   :{}

Actual value seems to be Error object here.

Test case for the bug itself:

const test = () => {
    throw new Error("Hi there");
};

describe("must.throw", () => {
    it("returns correct actual value", () => {
        try {
            test.must.throw(Error, "Hello world");
        }
        catch (e) {
            e.expected.must.equal("Hello world");
            e.actual.must.equal("Hi there");
        }
    });
});

This prints:

AssertionError: {"message":"Hi there"} must equal "Hi there"
Expected :"Hi there"
Actual   :{}