Analyzer 'Microsoft.Azure.WebJobs.Extensions.DurableTask.Analyzers.FunctionAnalyzer' threw an exception of type 'System.NullReferenceException'

Question

I get this warning while building my Azure functions project. There aren't much details in the the stack trace. Can anyone please help me make sense of this error?

> CSC : warning AD0001: Analyzer
> 'Microsoft.Azure.WebJobs.Extensions.DurableTask.Analyzers.FunctionAnalyzer'
> threw an exception of type 'System.NullReferenceException' with
> message 'Object reference not set to an instance of an object.'.

Here's the stacktrace if it helps:

> Severity  Code    Description Project File    Line    Suppression State   Detail
> Description Warning   AD0001  Analyzer
> 'Microsoft.Azure.WebJobs.Extensions.DurableTask.Analyzers.FunctionAnalyzer'
> threw an exception of type 'System.NullReferenceException' with
> message 'Object reference not set to an instance of an
> object.'. 
        1   Active  Analyzer
> 'Microsoft.Azure.WebJobs.Extensions.DurableTask.Analyzers.FunctionAnalyzer'
> threw the following exception: 'Exception occurred with following
> context: Compilation: 
> 
> System.NullReferenceException: Object reference not set to an instance
> of an object.    at
> Microsoft.Azure.WebJobs.Extensions.DurableTask.Analyzers.ArgumentAnalyzer.TryGetInputFromDurableContextCall(SemanticModel
> semanticModel, SyntaxNode definitionInput, SyntaxNode&
> inputFromContext)    at
> Microsoft.Azure.WebJobs.Extensions.DurableTask.Analyzers.ArgumentAnalyzer.TryGetDefinitionInputType(SemanticModel
> semanticModel, ActivityFunctionDefinition functionDefinition,
> ITypeSymbol& definitionInputType)    at
> Microsoft.Azure.WebJobs.Extensions.DurableTask.Analyzers.ArgumentAnalyzer.ReportProblems(CompilationAnalysisContext
> context, SemanticModel semanticModel, IEnumerable`1
> availableFunctions, IEnumerable`1 calledFunctions)    at
> Microsoft.Azure.WebJobs.Extensions.DurableTask.Analyzers.FunctionAnalyzer.RegisterAnalyzers(CompilationAnalysisContext
> context)    at
> Microsoft.CodeAnalysis.Diagnostics.AnalyzerExecutor.<>c.<ExecuteCompilationActionsCore>b__46_1(ValueTuple`2
> data)    at
> Microsoft.CodeAnalysis.Diagnostics.AnalyzerExecutor.ExecuteAndCatchIfThrows_NoLock[TArg](DiagnosticAnalyzer
> analyzer, Action`1 analyze, TArg argument, Nullable`1 info)
> ----- '.

Answer 1

The DurableTask Analyzer is a Roslyn analyzer that checks your code for inconsistencies when working with Durable Functions to help you prevent common mistakes. It is part of the DurableFunctions extension now.

Are you using the latest version of Durable Functions, v2.2.1? This version contains the most recent version of the DurableTask Analyzer v0.2.1 as a dependency and it appears there is a bug in there which causes the exception.

You could remove the Microsoft.Azure.WebJobs.Extensions.DurableTask.Analyzers dependency as a workaround to avoid getting this exception as follows:

• Go to your local folder where the DurableTask package is stored. For me this is: C:\Users\%User%\.nuget\packages\microsoft.azure.webjobs.extensions.durabletask\2.2.1
• Open the nuspec file and comment out (or remove) the two dependencies for Microsoft.Azure.WebJobs.Extensions.DurableTask.Analyzers, one for .NETFramework4.6.1, and one for .NETStandard2.0.
• Save the nuspec
• In your IDE, remove the package reference to the DurableTask extension.
• Add the DurableTask extension again. Since the package it's still in your local folder it should not download it from nuget.org. It will load the extension but not with the Analyzer now. It's hacky but it works.

I get the same error as you btw. I will check the issues at GitHub and will add a new one there if it hasn't been done yet.

Update: GH issue has been created.