What happens when you pass a `null` value to the `valueOf()` method?
If you pass a `null` value to the `valueOf()` method for a reference type, it will return `null` for `Boolean` and throw a `NullPointerException` for other types.
Satisfactory! `valueOf()` returns `null` only for certain wrapper types like `Boolean`, and throws `NullPointerException` for others.
Can you explain the exact behavior of `valueOf()` when passed `null` for types like `Integer` and `Double`?