Backend(Tests): extra safety measures against null #2951

Job	Run time
macOS--dotnet6-only	4m 3s
macOS--dotnet6-and-mono	7m 9s
windows--dotnet6-and-legacyFramework	5m 39s
macOS--mono-only	5m 7s
linux22-github--dotnet-and-mono	3m 35s
windows--dotnet6-only	5m 39s
windows--legacyFramework-only	7m 21s
linux22-github--dotnet-and-newmono	3m 48s
linux22-vanilla--newmono-only	5m 33s
linux22-vanilla--stockdotnet6-and-newmono	5m 27s
linux22-vanilla--stockdotnet6-only	4m 55s
linux22-vanilla--stockdotnet6-and-stockmono	4m 48s
linux22-vanilla--stockmono-only	4m 43s
linux20-github--dotnet-and-mono	3m 40s
linux20-vanilla--newmono-only	5m 36s
linux20-github--dotnet-and-newmono	3m 45s
linux20-vanilla--stockmono-only	5m 21s
conventions	1m 18s
snap_pkg	4m 1s
	1h 31m 28s

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