#46: Unexpectedly Found nil While Unwrapping an Optional

That error appears when code force-unwraps an optional with !, but the value is actually nil at runtime.

let text: String? = nil
print(text!) // crash

The fix is usually to unwrap safely:

if let text {
    print(text)
} else {
    print("Missing value")
}

You can also use guard let, optional chaining, or the nil-coalescing operator:

let name = text ?? "Anonymous"

Force unwrapping is only appropriate when nil is truly impossible and you are willing to treat violations as programmer errors.