How can I set a deeply nested value in Immutable.js?

Maps in Immutable have a setIn method that makes it easy to set deep values:

peopleImmutable = peopleImmutable.setIn(["Thomas", "nickname"], "Mr. T");

Or, using split to generate the array:

peopleImmutable = peopleImmutable.setIn("Thomas.nickname".split("."), "Mr. T");