Method add

frontend/src/utils/multi-map.ts:17–24

(key: K, value: V)

  }

  add(key: K, value: V): void {
    if (this.map.has(key)) {
      // oxlint-disable-next-line typescript/no-non-null-assertion
      this.map.get(key)!.push(value);
    } else {
      this.map.set(key, [value]);
    }
  }

  has(key: K): boolean {
    return this.map.has(key);