diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java
index 4c4addf5a673..296bce15c313 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java
@@ -1693,6 +1693,7 @@ public CodegenProperty fromProperty(String name, Schema p) {
         }
 
         if (p instanceof DateSchema || SchemaTypeUtil.DATE_FORMAT.equals(p.getFormat())) {
+            property.isString = false; // for backward compatibility with 2.x
             property.isDate = true;
             if (p.getEnum() != null) {
                 List<String> _enum = p.getEnum();
@@ -1710,6 +1711,7 @@ public CodegenProperty fromProperty(String name, Schema p) {
         }
 
         if (p instanceof DateTimeSchema || SchemaTypeUtil.DATE_TIME_FORMAT.equals(p.getFormat())) {
+            property.isString = false; // for backward compatibility with 2.x
             property.isDateTime = true;
             if (p.getEnum() != null) {
                 List<String> _enum = p.getEnum();
diff --git a/modules/openapi-generator/src/main/resources/qt5cpp/model-body.mustache b/modules/openapi-generator/src/main/resources/qt5cpp/model-body.mustache
index d903823911a6..7634ec32ed7f 100644
--- a/modules/openapi-generator/src/main/resources/qt5cpp/model-body.mustache
+++ b/modules/openapi-generator/src/main/resources/qt5cpp/model-body.mustache
@@ -220,7 +220,24 @@ bool
     bool isObjectUpdated = false;
     do{
     {{#vars}}
-        {{#isPrimitiveType}}if(m_{{name}}_isSet){ isObjectUpdated = true; break;}{{/isPrimitiveType}}{{#isContainer}}if({{name}}->size() > 0){ isObjectUpdated = true; break;}{{/isContainer}}{{^isContainer}}{{#complexType}}{{^isString}}{{^isDateTime}}if({{name}} != nullptr && {{name}}->isSet()){ isObjectUpdated = true; break;}{{/isDateTime}}{{/isString}}{{#isString}}if({{name}} != nullptr && *{{name}} != QString("")){ isObjectUpdated = true; break;}{{/isString}}{{/complexType}}{{/isContainer}}
+        {{#isPrimitiveType}}
+        if(m_{{name}}_isSet){ isObjectUpdated = true; break;}
+        {{/isPrimitiveType}}
+        {{#isContainer}}
+        if({{name}}->size() > 0){ isObjectUpdated = true; break;}
+        {{/isContainer}}
+        {{^isContainer}}
+        {{#complexType}}
+        {{^isString}}
+        {{^isDateTime}}
+        if({{name}} != nullptr && {{name}}->isSet()){ isObjectUpdated = true; break;}
+        {{/isDateTime}}
+        {{/isString}}
+        {{#isString}}
+        if({{name}} != nullptr && *{{name}} != QString("")){ isObjectUpdated = true; break;}
+        {{/isString}}
+        {{/complexType}}
+        {{/isContainer}}
     {{/vars}}
     }while(false);
     return isObjectUpdated;
diff --git a/samples/client/petstore/qt5cpp/client/SWGOrder.cpp b/samples/client/petstore/qt5cpp/client/SWGOrder.cpp
index 184856cdeb69..dd9c9a6b9a87 100644
--- a/samples/client/petstore/qt5cpp/client/SWGOrder.cpp
+++ b/samples/client/petstore/qt5cpp/client/SWGOrder.cpp
@@ -111,9 +111,6 @@ SWGOrder::asJsonObject() {
     if(m_quantity_isSet){
         obj.insert("quantity", QJsonValue(quantity));
     }
-    if(ship_date != nullptr && *ship_date != QString("")){
-        toJsonValue(QString("shipDate"), ship_date, obj, QString("QDateTime"));
-    }
     if(ship_date != nullptr) { 
         toJsonValue(QString("shipDate"), ship_date, obj, QString("QDateTime"));
     }
@@ -195,7 +192,6 @@ SWGOrder::isSet(){
         if(m_id_isSet){ isObjectUpdated = true; break;}
         if(m_pet_id_isSet){ isObjectUpdated = true; break;}
         if(m_quantity_isSet){ isObjectUpdated = true; break;}
-        if(ship_date != nullptr && *ship_date != QString("")){ isObjectUpdated = true; break;}
         if(status != nullptr && *status != QString("")){ isObjectUpdated = true; break;}
         if(m_complete_isSet){ isObjectUpdated = true; break;}
     }while(false);
diff --git a/samples/client/petstore/qt5cpp/client/SWGStoreApi.cpp b/samples/client/petstore/qt5cpp/client/SWGStoreApi.cpp
index c4e2b97f3c1f..37122be9f223 100644
--- a/samples/client/petstore/qt5cpp/client/SWGStoreApi.cpp
+++ b/samples/client/petstore/qt5cpp/client/SWGStoreApi.cpp
@@ -119,7 +119,7 @@ SWGStoreApi::getInventoryCallback(SWGHttpRequestWorker * worker) {
         msg = "Error: " + worker->error_str;
     }
 
-    QMap<QString, qint32>* output = NULL;
+    QMap<QString, qint32>* output = new QMap<QString, qint32>();
     QString json(worker->response);
     QByteArray array (json.toStdString().c_str());
     QJsonDocument doc = QJsonDocument::fromJson(array);