Fix NullReferenceException when connected to RavenDB cloud (#5112)

* Fix `NullReferenceException` when connected to RavenDB cloud which does not return memory information.

* Update src/ServiceControl.Audit.Persistence.RavenDB/MemoryInformationRetriever.cs

Co-authored-by: Mauro Servienti <[email protected]>

* use is null

---------

Co-authored-by: Mauro Servienti <[email protected]>

Author: ramonsmits

src/ServiceControl.Audit.Persistence.RavenDB/CustomChecks/CheckDirtyMemory.cs

@@ -8,7 +8,6 @@ namespace ServiceControl.Audit.Persistence.RavenDB.CustomChecks;
 
 class CheckDirtyMemory(MemoryInformationRetriever memoryInformationRetriever, ILogger<CheckDirtyMemory> logger) : CustomCheck("RavenDB dirty memory", "ServiceControl.Audit Health", TimeSpan.FromMinutes(5))
 {
-
     public override async Task<CheckResult> PerformCheck(CancellationToken cancellationToken = default)
     {
         var (isHighDirty, dirtyMemory) = await memoryInformationRetriever.GetMemoryInformation(cancellationToken);

src/ServiceControl.Audit.Persistence.RavenDB/MemoryInformationRetriever.cs

@@ -31,6 +31,8 @@ record MemoryInformation
         var httpResponse = await client.GetAsync("/admin/debug/memory/stats?includeThreads=false&includeMappings=false", cancellationToken);
         var responseDto = JsonSerializer.Deserialize<ResponseDto>(await httpResponse.Content.ReadAsStringAsync(cancellationToken));
 
-        return (responseDto.MemoryInformation.IsHighDirty, responseDto.MemoryInformation.DirtyMemory);
+        return responseDto.MemoryInformation is null
+            ? default
+            : (responseDto.MemoryInformation.IsHighDirty, responseDto.MemoryInformation.DirtyMemory);
     }
 }

src/ServiceControl.Persistence.RavenDB/MemoryInformationRetriever.cs

@@ -31,6 +31,8 @@ record MemoryInformation
         var httpResponse = await client.GetAsync("/admin/debug/memory/stats?includeThreads=false&includeMappings=false", cancellationToken);
         var responseDto = JsonSerializer.Deserialize<ResponseDto>(await httpResponse.Content.ReadAsStringAsync(cancellationToken));
 
-        return (responseDto.MemoryInformation.IsHighDirty, responseDto.MemoryInformation.DirtyMemory);
+        return responseDto.MemoryInformation is null
+            ? default
+            : (responseDto.MemoryInformation.IsHighDirty, responseDto.MemoryInformation.DirtyMemory);
     }
 }