Handle null values in array attributes

[alanwest]

Small follow on from #3262 to handle nulls in array attributes.

[codecov]

Codecov Report

Merging #3273 (70b640c) into main (e7f06af) will increase coverage by 0.17%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #3273      +/-   ##
==========================================
+ Coverage   85.39%   85.56%   +0.17%     
==========================================
  Files         263      263              
  Lines        9515     9520       +5     
==========================================
+ Hits         8125     8146      +21     
+ Misses       1390     1374      -16     

Impacted Files	Coverage Δ
...tryProtocol/Implementation/OtlpCommonExtensions.cs	100.00% <100.00%> (ø)
...ZPages/Implementation/ZPagesExporterEventSource.cs	56.25% <0.00%> (-6.25%)	⬇️
...emetry.Api/Internal/OpenTelemetryApiEventSource.cs	76.47% <0.00%> (-5.89%)	⬇️
...lemetry/Internal/SelfDiagnosticsConfigRefresher.cs	86.53% <0.00%> (-2.89%)	⬇️
...nTelemetry/Internal/OpenTelemetrySdkEventSource.cs	74.13% <0.00%> (-2.59%)	⬇️
...Telemetry/Internal/SelfDiagnosticsEventListener.cs	97.65% <0.00%> (+0.78%)	⬆️
...ter.ZPages/Implementation/ZPagesActivityTracker.cs	100.00% <0.00%> (+2.85%)	⬆️
...metryProtocol/Implementation/ActivityExtensions.cs	93.98% <0.00%> (+3.70%)	⬆️
...xporter.OpenTelemetryProtocol/OtlpTraceExporter.cs	77.27% <0.00%> (+40.90%)	⬆️
...entation/ExportClient/OtlpGrpcTraceExportClient.cs	78.57% <0.00%> (+42.85%)	⬆️