```typescript
export function mergeIntervals(intervals: number[][]): number[][] {
  if (!Array.isArray(intervals) || !intervals.every(pair => Array.isArray(pair) && pair.length === 2)) {
    throw new Error("Invalid input type");
  }

  intervals.sort((a, b) => a[0] - b[0]);

  const result: number[][] = [];
  let currentInterval = intervals[0];

  for (let i = 1; i < intervals.length; i++) {
    const nextInterval = intervals[i];
    if (currentInterval[1] >= nextInterval[0]) {
      currentInterval[1] = Math.max(currentInterval[1], nextInterval[1]);
    } else {
      result.push(currentInterval);
      currentInterval = nextInterval;
    }
  }

  result.push(currentInterval);

  return result.filter(interval => interval[0] <= interval[1]); // Remove invalid intervals
}
```