ExecutionStrategy.ShouldRetryOn receives a null argument with concurrency exceptions

[ixtreon]

The ExecutionStrategy base class automatically unwraps EF exceptions before passing them to the ShouldRetryOn method. The method which does the unwrapping, CallOnWrappedException, seems to directly recurse on the InnerException property of the parent exception without checking whether it is non-null.

This is not an issue if all instances of DbUpdateException have a non-null InnerException, but it seems that DbUpdateConcurrencyException exceptions thrown by the SQL Server and Sqlite providers don't include one. This causes such exceptions to be undetectable from the ShouldRetryOn method, when deriving from the ExecutionStrategy base class.

As this violates the [NotNull] attribute from the method's signature, this looks like a bug either with that method, or with the DbUpdateConcurrencyException type which doesn't have an InnerException.

Code to Reproduce

// DB Model
class User
{
    public int ID { get; set; }

    [ConcurrencyCheck]
    public string Email { get; set; }
}

class MyDbContext : DbContext
{
    public DbSet<User> Users { get; set; }

    public MyDbContext(DbContextOptions options)
        : base(options)
    {

    }
}

// Custom ExecutionStrategy
class CustomExecutionStrategy : ExecutionStrategy
{
    public CustomExecutionStrategy(DbContext context, int maxRetryCount, TimeSpan maxRetryDelay)
        : base(context, maxRetryCount, maxRetryDelay)
    { }

    protected override bool ShouldRetryOn(Exception exception)
    {
        if (exception == null)
            throw new Exception("Unexpected null exception");

        return exception is DbUpdateConcurrencyException;
    }
}

// NUnit test class

[TestFixture]
class ExecutionStrategyTests2
{

    DbContextOptions dbOptions;

    [SetUp]
    public void init()
    {
        // reuse same connection & db options as we want a single in-memory DB
        var connection = new SqliteConnection("DataSource=:memory:");
        connection.Open();

        dbOptions = new DbContextOptionsBuilder()
            .UseSqlite(connection)
            .UseLoggerFactory(LoggerFactory.Create(builder => builder.AddQueryDebug()))
            .EnableSensitiveDataLogging(true)
            .Options;

        // init DB and insert a single user
        var tempContext = new MyDbContext(dbOptions);
        tempContext.Database.EnsureCreated();

        tempContext.Set<User>().Add(new User
        {
            Email = "test@example.com",
        });
        tempContext.SaveChanges();
    }

    [Test]
    public void CustomExecutionStrategy_CatchesConcurrencyException()
    {
        var contextA = new MyDbContext(dbOptions);
        var strategy = new CustomExecutionStrategy(contextA, 3, TimeSpan.FromSeconds(5));
        var attemptsMade = 0;

        strategy.Execute(() =>
        {
            var entity = contextA.Set<User>().Single();

            // simulate a concurrency exception on first attempt only
            if (attemptsMade == 0)
            {
                var contextB = new MyDbContext(dbOptions);
                contextB.Set<User>().Single().Email = "second@example.com";
                contextB.SaveChanges();
            }
            attemptsMade++;

            entity.Email = "first@example.com";
            contextA.SaveChanges();
        });

        var tempContext = new MyDbContext(dbOptions);
        var entity5 = tempContext.Set<User>().Single();
    }
}

Results

Message: 
    System.Exception : Unexpected null exception
Stack Trace: 
    CustomExecutionStrategy.ShouldRetryOn(Exception exception) line 52
    ExecutionStrategy.ExecuteImplementation[TState,TResult](Func`3 operation, Func`3 verifySucceeded, TState state)
    ExecutionStrategyExtensions.Execute(IExecutionStrategy strategy, Action operation)
    ExecutionStrategyTests2.CustomExecutionStrategy_CatchesConcurrencyException() line 95

EF Core version: 3.1.9
Database provider: Microsoft.EntityFrameworkCore.SqlServer, Microsoft.EntityFrameworkCore.Sqlite
Target framework: .NET 4.6.1
Operating system: Windows 10
IDE: Visual Studio 2019 16.3.7