Remove coverage cache and handle empty files about web HOT 2 CLOSED

                  const browserUrl = `${url.pathname}${url.search}${url.hash}`;
                  let sources = cachedSources.get(browserUrl);
                  if (!sources) {
                    sources = await fetchSourceMap({
                        protocol: config.protocol,
                        host: config.hostname,
                        port: config.port,
                        browserUrl,
                        userAgent,
                    });
                    const originalSource = await readFile(filePath, 'utf8');
                    sources.originalSource = originalSource;
                    cachedSources.set(browserUrl, sources);
                  }
                  const converter = v8toIstanbul(filePath, 0, sources);
                  await converter.load();