我已将我的 Symfony 4 应用程序部署到 Google App Engine（灵活环境）。
构建似乎已经成功，但在 Chrome 中加载该应用程序会导致错误：
Oops! An Error Occurred
The server returned a "500 Internal Server Error".
Something is broken. Please let us know what you were doing when this error occurred. We will fix it as soon as possible. Sorry for any inconvenience caused.
应用引擎日志在这里：
2019/02/02 04:33:13 [info] 9#9: *6 client 172.17.0.4 closed keepalive connection
A
GET 404 191 B 0 ms Chrome 71 /favicon.ico A GET 404 191 B 0 ms Chrome 71
GET 500 930 B 6 ms Chrome 71 /connect/google A GET 500 930 B 6 ms Chrome 71
GET 307 316 B 6 ms Chrome 71 / A GET 307 316 B 6 ms Chrome 71
172.17.0.4 - - [02/Feb/2019:04:32:13 +0000] "GET /connect/google HTTP/1.1" 500 930 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36"
A
172.17.0.4 - - [02/Feb/2019:04:32:13 +0000] "GET / HTTP/1.1" 307 316 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36"
A
2019/02/02 04:29:08 [info] 9#9: *1 client 172.17.0.4 closed keepalive connection
A
GET 500 930 B 6 ms Chrome 71 /connect/google A GET 500 930 B 6 ms Chrome 71
GET 307 316 B 5 ms Chrome 71 / A GET 307 316 B 5 ms Chrome 71
172.17.0.4 - - [02/Feb/2019:04:28:08 +0000] "GET /connect/google HTTP/1.1" 500 930 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36"
A
172.17.0.4 - - [02/Feb/2019:04:28:08 +0000] "GET / HTTP/1.1" 307 316 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36"
A
GET 404 191 B 10 ms Chrome 71 /favicon.ico A GET 404 191 B 10 ms Chrome 71
GET 500 930 B 207 ms Chrome 71 /connect/google A GET 500 930 B 207 ms Chrome 71
172.17.0.4 - - [02/Feb/2019:04:27:50 +0000] "GET /connect/google HTTP/1.1" 500 930 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36"
A
GET 307 316 B 271 ms Chrome 71 / A GET 307 316 B 271 ms Chrome 71
172.17.0.4 - - [02/Feb/2019:04:27:49 +0000] "GET / HTTP/1.1" 307 316 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36"
A
A 2019-02-02 03:22:43,817 INFO success: nginx entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)
A 2019-02-02 03:22:43,817 INFO success: php-fpm entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)
A [02-Feb-2019 03:22:42] NOTICE: ready to handle connections
A [02-Feb-2019 03:22:42] NOTICE: fpm is running, pid 7
A 2019/02/02 03:22:42 [notice] 8#8: start worker process 9
A 2019/02/02 03:22:42 [notice] 8#8: start worker processes
A 2019/02/02 03:22:42 [notice] 8#8: getrlimit(RLIMIT_NOFILE): 65536:65536
A 2019/02/02 03:22:42 [notice] 8#8: OS: Linux 4.9.0-8-amd64
A 2019/02/02 03:22:42 [notice] 8#8: nginx/1.10.3 (Ubuntu)
A 2019/02/02 03:22:42 [notice] 8#8: using the "epoll" event method
A 2019-02-02 03:22:42,339 INFO spawned: 'nginx' with pid 8
A 2019-02-02 03:22:42,338 INFO spawned: 'php-fpm' with pid 7
A 2019-02-02 03:22:41,335 INFO supervisord started with pid 1
A 2019-02-02 03:22:41,329 WARN No file matches via include "/etc/supervisor/conf.d/*.conf"
A 2019-02-02 03:22:41,329 CRIT Supervisor running as root (no user in config file)
我不明白这个错误。我该如何解决？