Type of conditional expression cannot be determined because there is no implicit conversion between two objects with same base type

Question

I have read this stackoverflow topic:

Type of conditional expression cannot be determined because there is no implicit conversion between 'int' and <null>

I understand there is a risk of the compiler not understanding one of the types in ternary operator. However, my both classes inherit the same base class.

This is what I currently have:

public async Task Handle(IClientPendingIntegrationEvent message) {
    Command<Unit> command = _requestContext.SourceType == RequestSourceType.Backoffice
            ? new CreateManualUserEventCommand(message.UserId, eventType, UserEventDomain.Registration, message.Reason)
            : new CreateUserEventCommand(message.UserId, eventType, UserEventOriginType.System, UserEventDomain.Registration, message.Reason);

    await _mediator.Send(command);
}


public class CreateManualUserEventCommand : Command<Unit>
{
    public CreateManualUserEventCommand(
        string userId,
        UserEventType userEventType,
        UserEventDomain domain,
        string comment = null)
    {
        UserId = userId;
        Type = userEventType;
        Domain = domain;
        Comment = comment;
    }

    public string UserId { get; private set; }

    public UserEventType Type { get; private set; }

    public UserEventDomain Domain { get; private set; }

    public string Comment { get; private set; }
}


public class CreateUserEventCommand : Command<Unit>
    {
        public CreateUserEventCommand(
            string userId,
            UserEventType type,
            UserEventOriginType createdByOrigin,
            UserEventDomain domain,
            string comment = null)
        {
            UserId = userId;
            Type = type;
            CreatedByOrigin = createdByOrigin;
            Domain = domain;
            Comment = comment;
        }

        public string UserId { get; }

        public UserEventType Type { get; }

        public UserEventOriginType CreatedByOrigin { get; }

        public UserEventDomain Domain { get; }

        public string Comment { get; }
    }

This is the exact error the compiler throws.

Error CS0173: Type of conditional expression cannot be determined because there is no implicit conversion between

'MFG.Auditing.Application.Features.Backoffice.UserEvents.Commands.CreateManualUserEvent.CreateManualUserEventCommand' and 'MFG.Auditing.Application.Features.System.UserEvents.Commands.CreateUserEvent.CreateUserEventCommand'

I understand that I can easily rework this with if and else but I need to use ternary operator here.