```typescript
const MODULUS = 1000000007;

/** The nth Fibonacci number, modulo 1000000007. */
export function fibMod(n: number): number {
  if (typeof n !== 'number' || n < 0 || Math.floor(n) !== n) {
    throw new Error('Input must be a non-negative integer');
  }
  let a = 0, b = 1;
  for (let i=0;i<n;i++) {
      [a,b] = [(a+b)%MODULUS, a];
  }
  return a;
}
```