LogManager.GetCurrentClassLogger can throw a NullReferenceException in .Net Core/.Net 5.0.

[rmjcsltd]

Unfortunately I can't provide a simple way to reproduce this but in the codebase I'm working with the error occured repeatedly until the call to GetCurrentClassLogger was replaced with GetLogger("SomeName").

I'm working with WebJobs in a .Net Core Azure App Service. Here's the complete unmodified stack trace;

Object reference not set to an instance of an object. System.NullReferenceException: Object reference not set to an instance of an object.
   at CorrelatorSharp.Logging.LogManager.GetCurrentClassLogger()
   at ResolveService(ILEmitResolverBuilderRuntimeContext , ServiceProviderEngineScope )
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService(Type serviceType)
   at Microsoft.Extensions.DependencyInjection.ActivatorUtilities.GetService(IServiceProvider sp, Type type, Type requiredBy, Boolean isDefaultParameterRequired)
   at lambda_method(Closure , IServiceProvider , Object[] )
   at Microsoft.Azure.WebJobs.Host.Executors.DefaultJobActivator.CreateInstance[T](IServiceProvider serviceProvider) in C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\DefaultJobActivator.cs:line 37
   at Microsoft.Azure.WebJobs.Host.Executors.DefaultJobActivator.CreateInstance[T](IFunctionInstanceEx functionInstance) in C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\DefaultJobActivator.cs:line 32
   at Microsoft.Azure.WebJobs.Host.Executors.ActivatorInstanceFactory`1.<>c__DisplayClass1_1.<.ctor>b__0(IFunctionInstanceEx i) in C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\ActivatorInstanceFactory.cs:line 20
   at Microsoft.Azure.WebJobs.Host.Executors.ActivatorInstanceFactory`1.Create(IFunctionInstanceEx functionInstance) in C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\ActivatorInstanceFactory.cs:line 26
   at Microsoft.Azure.WebJobs.Host.Executors.FunctionInvoker`2.CreateInstance(IFunctionInstanceEx functionInstance) in C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionInvoker.cs:line 44
   at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.ParameterHelper.Initialize() in C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs:line 796
   at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.TryExecuteAsyncCore(IFunctionInstanceEx functionInstanceEx, CancellationToken cancellationToken, ILogger logger) in C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs:line 145

Interestingly, the method calling GetCurrentClassLogger isn't in the stack trace, it's just a simple class constructor, nothing fancy. This puzzled me at first but some Googling showed that method inlining either by the source compiler or the JIT compiler can cause this.

According to the MS docs for .Net Core 3.1 & .Net 5.0 MemberInfo.DeclaringType returns nullable Type? so this could be the cause. For both .Net Framework 4.8 and .Net Standard it returns Type.