```ts
const MODULUS = 1000000007;

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

  const memo: number[] = new Array(n + 1);
  memo[0] = 0;
  memo[1] = 1;

  for (let i = 2; i <= n; i++) {
    memo[i] = (memo[i - 1] + memo[i - 2]) % MODULUS;
  }

  return memo[n];
}
```