dispatcher inner exception

dotnet/AipsCore/Application/Common/Dispatcher/DispatchException.cs

@@ -5,7 +5,7 @@ namespace AipsCore.Application.Common.Dispatcher;
 
 public class DispatchException : Exception
 {
-    public DispatchException(object commandQuery)
-        : base($"Error while dispatching '{commandQuery.GetType().Name}'")
+    public DispatchException(object commandQuery, Exception innerException)
+        : base($"Error dispatching '{commandQuery.GetType().Name}' because of: {innerException.Message}", innerException)
     { }
 }

dotnet/AipsCore/Application/Common/Dispatcher/Dispatcher.cs

@@ -59,11 +59,15 @@ public sealed class Dispatcher : IDispatcher
 
     private dynamic ResolveHandler(Type handlerType, object commandOrQuery)
     {
-        dynamic? handler = _serviceProvider.GetService(handlerType);
-        
-        if (handler is null)
+        dynamic handler;
+
+        try
         {
-            throw new DispatchException(commandOrQuery);
+            handler = _serviceProvider.GetRequiredService(handlerType);
+        }
+        catch (InvalidOperationException serviceProviderException)
+        {
+            throw new DispatchException(commandOrQuery, serviceProviderException);
         }
 
         return handler;