evaluating mysql NULL with = operator - c++

Question

I have following Qt/C++ class method:
bool UeOrdersModel::ueSlotRefreshOrdersData(const QString& userId,
const QString& placeId,
const QString& customerId)
{
bool result=false;
bool connected=false;
bool customerIdEmpty=customerId.isEmpty()||customerId.isNull();
this->ueSetUserId(userId);
this->ueSetPlaceId(placeId);
if(this->ueDatabase().isOpen())
{
connected=true;
}
else
{
if(this->ueConnectToDatabase())
{
connected=this->ueDatabase().open();
} // if
} // if
if(connected)
{
this->setQuery(UePosDatabase::UeSqlQueries::UeViewOrders::SQL_QUERY_GET_ORDERS_FILTERED_BY_USERID_PLACEID_CUSTOMER_ID.arg(userId)
.arg(placeId)
.arg(customerIdEmpty?QString(QString::null):customerId),
this->ueDatabase());
if(this->query().lastError().isValid())
{
qDebug() << Q_FUNC_INFO
<< this->query().lastError().text();
}
else
{
this->ueUpdateTotalAmounts(userId,
placeId,
customerId);
result=true;
} // if
}
else
{
qDebug() << Q_FUNC_INFO
<< this->lastError().text();
} // if
return result;
} // ueSlotRefreshOrdersData
which basically executes following mysql query:
static const QString SQL_QUERY_GET_ORDERS_FILTERED_BY_USERID_PLACEID_CUSTOMER_ID=
"SELECT ORDERS.USER_ID, PEOPLE.NAME, PLACE_ID, PLACES.NAME, PRODUCT_ID, "
"PRODUCTS.IMAGE, PRODUCTS.NAME, PRODUCTS.PRICESELL, TAXES.RATE, ORDERS.PRODUCT_QUANTITY, ORDERS.CUSTOMER_ID "
"FROM ORDERS "
"JOIN PEOPLE ON ORDERS.USER_ID=PEOPLE.ID "
"JOIN PRODUCTS ON ORDERS.PRODUCT_ID=PRODUCTS.ID "
"JOIN PLACES ON ORDERS.PLACE_ID=PLACES.ID "
"JOIN TAXCATEGORIES ON PRODUCTS.TAXCAT=TAXCATEGORIES.ID "
"JOIN TAXES ON TAXCATEGORIES.ID=TAXES.ID "
"WHERE ORDERS.USER_ID=\"%1\" AND ORDERS.PLACE_ID=\"%2\" AND CUSTOMER_ID=\"%3\"";
Now, if method's third parameter, customerId, is empty, I must evaluate upper mysql statement with CUSTOMER IS NULL, I am aware of that. But, is it possible to evaluate mysql NULL value using = operator, like in my case?