```ts
const MODULUS = 1000000007;

/**
 * The nth Fibonacci number, modulo 1000000007.
 */
export function fibMod(n: number): number {
  if (typeof n !== 'number' || n < 0) {
    throw new Error('input must be a non-negative integer');
  } else if (n % 1 !== 0) {
    throw new Error('input must be an integer');
  }

  let r = 0;
  let x = 1;
  let y = 0;

  for (let _ = 2; _ <= n; _++) {
    [r, x] = [x + y, r];
  }
  
  return (r % MODULUS + MODULUS) % MODULUS;
}
```