```typescript
const MODULUS = 1000000007;

/** The nth Fibonacci number, modulo 1000000007. */
export function fibMod(n: number): number {
  if (typeof n !== 'number' || !Number.isInteger(n) || n < 0) {
    throw new Error('Input must be a non-negative integer');
  }

  let first = 0;
  let second = 1;

  for (let i = 2; i <= n; i++) {
    if (first % MODULUS === 0 && first % MODULUS === 0) break;
    const tmp = first + second;
    first = second;
    second = tmp % MODULUS;
  }

  return first;
}
```