```ts
const MODULUS = 1000000007;

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

  const memo: { [key: number]: number } = { 0: 0, 1: 1 };

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

  return memo[n];
}
```