private IHandler <T> GetHandler <T>()
{
var handlers = handlerFactory.GetForCommand <T>();
if (handlers.Count == 0)
{
throw new CommandHandlerNotFoundException(typeof(T));
}
if (handlers.Count > 1)
{
throw new NonExclusiveCommandHandlerException(typeof(T), handlers.Select(x => x.GetType()));
}
var handler = handlers.Single();
return(handler);
}