I apllied the following fix:

        case 'joined_entries':
            $iJoinedProfileId = $aParams['joined_profile'] ?? null;
            $oJoinedProfile = $iJoinedProfileId ? BxDolProfile::getInstance((int)$iJoinedProfileId) : null;
            if (!$oJoinedProfile) {
                $this->isError = true;
                break;
            }