Variable type incorrectly narrowed to null when a callback is passed to a function #15380

class Foo {
    public bar: string = "";
}

function test() {
    let foo: Foo | null = null;

    [1].forEach((item) => {
        foo = new Foo();
    });

    // Here Typescript compiler incorrectly thinks that 'foo' has null type 
    // although it will always be an instance of Foo class.
    if (foo) {
        // The next line does not compile because 'foo' variable has never type here.
        foo.bar;
    }
}

class Foo {
    public bar: string = "";
}

function test() {
    let foo: Foo | null = null;

    // When calling a simple lambda explicitly this works as expected
    (() => {
        foo = new Foo();
    })();
    if (foo) {
        foo.bar;
    }
}