fixed return value

nucleus/principalNetworkDomain.go

@@ -45,7 +45,7 @@ func NewPND(name, description string, id uuid.UUID, sbi SouthboundInterface) (Pr
 		id:          id,
 	}
 	if err := pnd.sbic.add(sbi); err != nil {
-		return nil, &ErrAlreadyExists{item: sbi}
+		return nil, err
 	}
 	return pnd, nil
 }