Immutable.js TypeScript issues

foo.ts

{
    // Parameter types should not be nullable
    // https://github.com/facebook/immutable-js/pull/919
    const xs: List<number> = List([1])
    xs.forEach(x => {
        x // number | undefined, should be number
    })
    // Workaround:
    xs.forEach((x: number) => {
        x // number
    })
}
{
    // Operators return wrong type
    const xs: List<number> = List([1])
    const xsPlus1A: List<number> = xs.map(x => x + 1) // Type 'Iterable<number, number>' is not assignable to type 'List<number>'.
    // Workaround:
    const xsPlus1B: List<number> = xs.map(x => x + 1).toList()
}
{
    // Map key/value cannot be inferred
    // https://github.com/facebook/immutable-js/issues/686
    const mapA: Map<string, string> = Map([[ 'foo', 'bar' ]]) // Type 'Map<{}, {}>' is not assignable to type 'Map<string, string>'.
    // Workaround:
    const mapB: Map<string, string> = Map<string, string>([[ 'foo', 'bar' ]])
}
{
    // Get should return nullable type
    const xs: List<number> = List([1])
    const maybeXA = xs.get(0)
    maybeXA // number, should be number | undefined
    // Workaround:
    const maybeXB: number | undefined = xs.get(0);
    maybeXB // number | undefined
}