Return nth Fibonacci Recursion Challenge

Given a non-negative integer n, return the Fibonacci number at that index. The Fibonacci sequence is [0, 1, 1, 2, 3, 5, 8, 13, 21, ...] where index 0 is 0 and index 1 is 1. If n is negative, return null.

Function Signature

nthFibo(n)

Parameters

• n — an integer representing the index in the Fibonacci sequence.

Output

Return a number representing the Fibonacci value at index n, or null if n is negative.

Constraints

• The function must use recursion.
• The function should accept exactly one argument.

Examples

nthFibo(0)  → 0
nthFibo(1)  → 1
nthFibo(2)  → 1
nthFibo(3)  → 2
nthFibo(5)  → 5
nthFibo(8)  → 21
nthFibo(-5) → null