Crash on iPad [GAD_GADUserPreferences_arm64_8_9_0]

[Joey]

Hi, my app in production get many crashes with google ad sdk (AD_GADUserPreferences_arm64_8_9_0). We cannot reproduced this bug. This is crash log.

Thank you for your investigation.

Device: iPad

iOS: 14, 15

GoogleMobileAdsSDK: 8.9.0

```

Crashed: com.apple.root.default-qos

0  libsystem_platform.dylib       0x1884 _platform_strlen + 4

1  MoneyApp                        0x278130 gd_hc + 4338188592

2  MoneyApp                        0x278338 gd_hi + 4338189112

3  MoneyApp                        0x2782b8 gd_hi + 4338188984

4  MoneyApp                        0x224e78 gad_hi + 4337847928

5  MoneyApp                        0x32309c GAD_GADUserPreferences_arm64_8_9_0 + 4338888860

6  libdispatch.dylib              0x1e60 _dispatch_call_block_and_release + 32

7  libdispatch.dylib              0x3bac _dispatch_client_callout + 20

8  libdispatch.dylib              0x6cd4 _dispatch_queue_override_invoke + 792

9  libdispatch.dylib              0x1531c _dispatch_root_queue_drain + 396

10 libdispatch.dylib              0x15b58 _dispatch_worker_thread2 + 164

11 libsystem_pthread.dylib        0x3574 _pthread_wqthread + 228

12 libsystem_pthread.dylib        0x22c4 start_wqthread + 8

```