### String Rotate Right

Geoffrey Challen // 2020.9.1

This problem combines `String`s, functions, and arrays. Super fun!

Write a function called `rotateRight` that takes a nullable `String` as its first argument and a non-negative `Int` as its second argument and rotates the `String` by the given number of characters. Here's what we mean by rotate:

• `CS125` rotated right by 1 becomes `5CS12`
• `CS125` rotated right by 2 becomes `25CS1`
• `CS125` rotated right by 3 becomes `125CS`
• `CS125` rotated right by 4 becomes `S125C`
• `CS125` rotated right by 5 becomes `CS125`
• `CS125` rotated right by 8 becomes `125CS`

And so on. Notice how characters rotated off the right end of the `String` wrap around to the left.

This problem is tricky! Here are a few hints:

1. You will want to use the remainder operator to perform modular arithmetic.
2. You will probably want to convert the `String` to an array of characters before you begin.
3. You can convert an array of characters `characters` back into a `String` like this: `String(characters)`.
4. You can also solve this problem quite elegantly using `substring`.

If the passed `String` argument is `null`, you should return `null`. Good luck and have fun!