Applying proxy or Scoped decorators using decorator type factory fails with NullReferenceException on uncontrolled collections.

[dotnetjunkie]

Simple Injector blocks the application of both Scoped decorators and proxy decorators to container uncontrolled collections. However, when such decorator registration is made using the overload that takes in a decorator type factory, Simple Injector throws a rather obscure NullReferenceException, instead of throwing the expected descriptive exception.

The following tests reproduce the issue:

sealed class PluginProxy : IPlugin
{
    public PluginProxy(Func<IPlugin> pluginFactory) { }
}

sealed class PluginDecorator : IPlugin
{
    public PluginDecorator(IPlugin plugin) { }
}

[TestMethod]
public void Test1()
{
    // Act
    var container = new Container();

    IEnumerable<IPlugin> collection = new[] { new PluginImpl() };

    container.Collection.Register(containerUncontrolledCollection: collection);
    container.RegisterDecorator(
        typeof(IPlugin),
        _ => typeof(PluginProxy), // factory returning (func-wrapping) proxy
        Lifestyle.Transient,
        _ => true);

    // Act
    Action action = () => container.Verify(); // Currently fails with a NullReferenceException

    // Assert
    AssertThat.ThrowsWithExceptionMessageContains<InvalidOperationException>(
        "It's impossible for the container to generate a Func<IPlugin> for injection into the " +
        "PluginProxy decorator that will be wrapped around instances of the collection of IPlugin " +
        "instances",
        action);
}

[TestMethod]
public void Test2()
{
    // Act
    var container = new Container();
    container.Options.DefaultScopedLifestyle = new AsyncScopedLifestyle();

    IEnumerable<IPlugin> collection = new[] { new PluginImpl() };

    container.Collection.Register(containerUncontrolledCollection: collection);
            
    container.RegisterDecorator(
        typeof(IPlugin),
        _ => typeof(PluginDecorator), // using factory
        Lifestyle.Scoped, // lifestyle other than singleton or transient
        _ => true);

    // Act
    Action action = () => container.Verify(); // Currently fails with a NullReferenceException

    // Assert
    AssertThat.ThrowsWithExceptionMessageContains<InvalidOperationException>(
        "You are trying to apply the PluginDecorator decorator with the 'Async Scoped' lifestyle " +
        "to a collection of type IPlugin, but the registered collection is not controlled by the " +
        "container.",
        action);
}

[dotnetjunkie]

bug-703 branch created.