This Python async function has 3 bugs: a race condition, an unhandled exception, and a resource leak. Find all three and explain why each is problematic. ```python import asyncio import aiohttp class DataFetcher: def __init__(self): self.cache = {} self.session = aiohttp.ClientSession() async def fetch_data(self, urls): results = [] for url in urls: if url in self.cache: results.append(self.cache[url]) else: async with self.session.get(url) as response: data = await response.json() self.cache[url] = data results.append(data) return results async def fetch_parallel(self, urls): tasks = [self.fetch_single(url) for url in urls] return await asyncio.gather(*tasks) async def fetch_single(self, url): if url in self.cache: return self.cache[url] async with self.session.get(url) as response: data = await response.json() self.cache[url] = data return data ```