[devicelab] work around occasional null values for devtools (#69273)
[devicelab] work around occasional null values for devtools (#69273)

* [devicelab] work around occasional null values for devtools

* Update perf_tests.dart
tvolkert/flutter,Hixie/flutter,Hixie/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter,flutter/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,flutter/flutter,tvolkert/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,flutter/flutter,flutter/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter