I'm seeing the same thing. Several warnings in Visual Studio:
CSC : warning AD0001: Analyzer 'Microsoft.AspNetCore.Mvc.Analyzers.TopLevelParameterNameAnalyzer' threw an exception of type 'System.NullReferenceException' with message 'Object reference not set to an instance of an object.'.
Per the following discussion, it appears that the cause is nuget packages which have a 2.2 dependency.
https://github.com/dotnet/aspnetcore/issues/14723
jsreport.AspNetCore 2.0.2 references a couple of 2.2 packages and this appears to be the source of warnings in my project.