```typescript
const MODULUS = 1000000007;

export function fibMod(n: number): number {
  if (typeof n !== "number" || n < 0) {
    throw new Error("n must be a non-negative integer");
  }

  let a = 0;
  let b = 1;
  let result = 0;

  if (n === 0) {
    return 0;
  } else if (n === 1) {
    return 1;
  }

  for (let _ = 2; _ <= n; _++) {
    const temp = (a + b) % MODULUS;
    a = b;
    b = temp;

    if (b >= MODULUS) {
      b -= MODULUS;
    }
  }

  return b;
}
```