```ts
export function mergeIntervals(intervals: number[][]): number[][] {
  if (!intervals.every(([start, end]) => typeof start === 'number' && typeof end === 'number')) {
    throw new Error('All intervals must have numeric start and end values.');
  }

  // Sort intervals by start value
  const sortedIntervals = [...intervals].sort((a, b) => a[0] - b[0]);

  // Merge overlapping intervals
  const merged: number[][] = [];
  let currentInterval = sortedIntervals[0];

  for (let i = 1; i < sortedIntervals.length; i++) {
    const nextInterval = sortedIntervals[i];

    if (currentInterval[1] >= nextInterval[0]) {
      // Merge intervals
      currentInterval[1] = Math.max(currentInterval[1], nextInterval[1]);
    } else {
      // Add the current interval to the merged list and start a new one
      merged.push([...currentInterval]);
      currentInterval = nextInterval;
    }
  }

  // Add the last merged interval
  merged.push([...currentInterval]);

  return merged;
}
```