Backend: handle null response from Eth server #3976

Job	Run time
macOS--mono-only	5m 50s
windows--dotnet6-and-legacyFramework	5m 0s
linux22-github--dotnet-and-mono	3m 48s
linux22-vanilla--stockmono-only	5m 36s
linux22-github--dotnet-and-newmono	4m 21s
linux22-vanilla--stockdotnet6-only	5m 0s
macOS--dotnet6-and-mono	6m 43s
macOS--dotnet6-only	5m 53s
windows--dotnet6-only	6m 12s
windows--legacyFramework-only	11m 55s
linux20-github--dotnet-and-mono	4m 11s
linux20-github--dotnet-and-newmono	4m 21s
linux20-vanilla--newmono-only	6m 27s
linux20-vanilla--stockmono-only	5m 51s
linux22-vanilla--newmono-only	6m 25s
linux22-vanilla--stockdotnet6-and-newmono	6m 17s
linux22-vanilla--stockdotnet6-and-stockmono	5m 16s
conventions	1m 16s
snap_pkg	4m 30s
	1h 44m 52s

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