Skip unknown/removed commands still queued in the database

src/NzbDrone.Core.Test/Datastore/Converters/CommandConverterFixture.cs

@@ -3,6 +3,7 @@ using FluentAssertions;
 using NUnit.Framework;
 using NzbDrone.Core.Books.Commands;
 using NzbDrone.Core.Datastore.Converters;
+using NzbDrone.Core.Messaging.Commands;
 using NzbDrone.Core.Test.Framework;
 
 namespace NzbDrone.Core.Test.Datastore.Converters
@@ -42,6 +43,14 @@ namespace NzbDrone.Core.Test.Datastore.Converters
             Subject.Parse(data).Should().BeOfType<RefreshAuthorCommand>();
         }
 
+        [Test]
+        public void should_return_unknown_command_when_getting_json_from_db()
+        {
+            var data = "{\"name\": \"EnsureMediaCovers\"}";
+
+            Subject.Parse(data).Should().BeOfType<UnknownCommand>();
+        }
+
         [Test]
         public void should_return_null_for_null_value_when_getting_from_db()
         {

src/NzbDrone.Core/Datastore/Converters/CommandConverter.cs

@@ -27,7 +27,11 @@ namespace NzbDrone.Core.Datastore.Converters
 
             if (impType == null)
             {
-                throw new CommandNotFoundException(contract);
+                var result = JsonSerializer.Deserialize<UnknownCommand>(stringValue, SerializerSettings);
+
+                result.ContractName = contract;
+
+                return result;
             }
 
             return (Command)JsonSerializer.Deserialize(stringValue, impType, SerializerSettings);

src/NzbDrone.Core/Messaging/Commands/CommandExecutor.cs

@@ -69,8 +69,7 @@ namespace NzbDrone.Core.Messaging.Commands
 
             try
             {
-                var handlerContract = typeof(IExecute<>).MakeGenericType(command.GetType());
-                handler = (IExecute<TCommand>)_serviceFactory.Build(handlerContract);
+                handler = (IExecute<TCommand>)_serviceFactory.Build(typeof(IExecute<TCommand>));
 
                 _logger.Trace("{0} -> {1}", command.GetType().Name, handler.GetType().Name);
 

src/NzbDrone.Core/Messaging/Commands/UnknownCommand.cs

@@ -0,0 +1,11 @@
+namespace NzbDrone.Core.Messaging.Commands
+{
+    public class UnknownCommand : Command
+    {
+        public override bool SendUpdatesToClient => false;
+
+        public override string CompletionMessage => "Skipped";
+
+        public string ContractName { get; set; }
+    }
+}

src/NzbDrone.Core/Messaging/Commands/UnknownCommandExecutor.cs

@@ -0,0 +1,24 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using NLog;
+
+namespace NzbDrone.Core.Messaging.Commands
+{
+    public class UnknownCommandExecutor : IExecute<UnknownCommand>
+    {
+        private readonly Logger _logger;
+
+        public UnknownCommandExecutor(Logger logger)
+        {
+            _logger = logger;
+        }
+
+        public void Execute(UnknownCommand message)
+        {
+            _logger.Debug("Ignoring unknown command {0}", message.ContractName);
+        }
+    }
+}