When service is not registered, unhelpful NullReferenceException is thrown instead of InvalidOperationException

[JarkoDubbeldam]

Describe the Bug

When using AutofacWebServiceHostFactory to create a service, when that service is not registered in the container, results in an unhelpful NRE, instead of throwing the intended InvalidOperationException (

Autofac.Wcf/src/Autofac.Integration.Wcf/DefaultServiceImplementationDataProvider.cs

Line 85 in 1987b3e

throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, AutofacHostFactoryResources.ServiceNotRegistered, value));

).

Steps to Reproduce

See this minimal working example project: https://github.com/JarkoDubbeldam/Autofac.Integraction.Wcf.BugRepro/blob/master/BugRepro/ServiceHostFactory.cs

Expected Behavior

I'd expect a more helpful error :)

Exception with Stack Trace

System.NullReferenceException
  HResult=0x80004003
  Message=Object reference not set to an instance of an object.
  Source=Autofac.Integration.Wcf
  StackTrace:
   at Autofac.Integration.Wcf.DefaultServiceImplementationDataProvider.GetServiceImplementationData(String value)
   at Autofac.Integration.Wcf.AutofacHostFactory.CreateServiceHost(String constructorString, Uri[] baseAddresses)
   at BugRepro.ServiceHostFactory.CreateServiceHost(String constructorString, Uri[] baseAddresses) in C:\Users\jdubbeldam\source\repos\BugRepro\BugRepro\ServiceHostFactory.cs:line 17

Dependency Versions

<packages>
  <package id="Autofac" version="6.0.0" targetFramework="net472" />
  <package id="Autofac.Wcf" version="6.0.0" targetFramework="net472" />
  <package id="Microsoft.Bcl.AsyncInterfaces" version="1.1.0" targetFramework="net472" />
  <package id="System.Buffers" version="4.5.1" targetFramework="net472" />
  <package id="System.Diagnostics.DiagnosticSource" version="4.7.1" targetFramework="net472" />
  <package id="System.Memory" version="4.5.4" targetFramework="net472" />
  <package id="System.Numerics.Vectors" version="4.5.0" targetFramework="net472" />
  <package id="System.Runtime.CompilerServices.Unsafe" version="4.5.3" targetFramework="net472" />
  <package id="System.Threading.Tasks.Extensions" version="4.5.2" targetFramework="net472" />
</packages>

Additional Info

It appears to me that this statement can never be true, due to serviceRegistration not being nullable.