The First Lonely Letter

In a word full of repeats, find the first letter that appears exactly ONCE — the introvert of the word. 🧍

You get a word. Print its first never-repeated letter, or none.

Example:

Input: word = "swiss" Output: w

Tallying gives s=3, w=1, i=1. Walking the word in order, "w" is the first letter whose count is exactly 1.