diff --git a/modules/openapi-generator/src/main/resources/cpp-pistache-server/model-source.mustache b/modules/openapi-generator/src/main/resources/cpp-pistache-server/model-source.mustache
index c58a2fc79a0..e69d65cafc6 100644
--- a/modules/openapi-generator/src/main/resources/cpp-pistache-server/model-source.mustache
+++ b/modules/openapi-generator/src/main/resources/cpp-pistache-server/model-source.mustache
@@ -37,7 +37,7 @@ void to_json(nlohmann::json& j, const {{classname}}& o)
 void from_json(const nlohmann::json& j, {{classname}}& o)
 {
     {{#vars}}
-    {{#required}}j.at("{{baseName}}").get_to(o.m_{{name}});{{/required}}{{^required}}if(j.contains("{{baseName}}"))
+    {{#required}}j.at("{{baseName}}").get_to(o.m_{{name}});{{/required}}{{^required}}if(j.find("{{baseName}}") != j.end())
     {
         j.at("{{baseName}}").get_to(o.m_{{name}});
         o.m_{{name}}IsSet = true;
diff --git a/samples/server/petstore/cpp-pistache/model/ApiResponse.cpp b/samples/server/petstore/cpp-pistache/model/ApiResponse.cpp
index a78fb1cc7f9..77cd466e145 100644
--- a/samples/server/petstore/cpp-pistache/model/ApiResponse.cpp
+++ b/samples/server/petstore/cpp-pistache/model/ApiResponse.cpp
@@ -51,17 +51,17 @@ void to_json(nlohmann::json& j, const ApiResponse& o)
 
 void from_json(const nlohmann::json& j, ApiResponse& o)
 {
-    if(j.contains("code"))
+    if(j.find("code") != j.end())
     {
         j.at("code").get_to(o.m_Code);
         o.m_CodeIsSet = true;
     } 
-    if(j.contains("type"))
+    if(j.find("type") != j.end())
     {
         j.at("type").get_to(o.m_Type);
         o.m_TypeIsSet = true;
     } 
-    if(j.contains("message"))
+    if(j.find("message") != j.end())
     {
         j.at("message").get_to(o.m_Message);
         o.m_MessageIsSet = true;
diff --git a/samples/server/petstore/cpp-pistache/model/Category.cpp b/samples/server/petstore/cpp-pistache/model/Category.cpp
index 2abb0c3c5e2..43ff1d49000 100644
--- a/samples/server/petstore/cpp-pistache/model/Category.cpp
+++ b/samples/server/petstore/cpp-pistache/model/Category.cpp
@@ -47,12 +47,12 @@ void to_json(nlohmann::json& j, const Category& o)
 
 void from_json(const nlohmann::json& j, Category& o)
 {
-    if(j.contains("id"))
+    if(j.find("id") != j.end())
     {
         j.at("id").get_to(o.m_Id);
         o.m_IdIsSet = true;
     } 
-    if(j.contains("name"))
+    if(j.find("name") != j.end())
     {
         j.at("name").get_to(o.m_Name);
         o.m_NameIsSet = true;
diff --git a/samples/server/petstore/cpp-pistache/model/Inline_object.cpp b/samples/server/petstore/cpp-pistache/model/Inline_object.cpp
index ebb31303908..89638a84566 100644
--- a/samples/server/petstore/cpp-pistache/model/Inline_object.cpp
+++ b/samples/server/petstore/cpp-pistache/model/Inline_object.cpp
@@ -47,12 +47,12 @@ void to_json(nlohmann::json& j, const Inline_object& o)
 
 void from_json(const nlohmann::json& j, Inline_object& o)
 {
-    if(j.contains("name"))
+    if(j.find("name") != j.end())
     {
         j.at("name").get_to(o.m_Name);
         o.m_NameIsSet = true;
     } 
-    if(j.contains("status"))
+    if(j.find("status") != j.end())
     {
         j.at("status").get_to(o.m_Status);
         o.m_StatusIsSet = true;
diff --git a/samples/server/petstore/cpp-pistache/model/Inline_object_1.cpp b/samples/server/petstore/cpp-pistache/model/Inline_object_1.cpp
index d5ffe1fef88..0da3bdba2b8 100644
--- a/samples/server/petstore/cpp-pistache/model/Inline_object_1.cpp
+++ b/samples/server/petstore/cpp-pistache/model/Inline_object_1.cpp
@@ -46,12 +46,12 @@ void to_json(nlohmann::json& j, const Inline_object_1& o)
 
 void from_json(const nlohmann::json& j, Inline_object_1& o)
 {
-    if(j.contains("additionalMetadata"))
+    if(j.find("additionalMetadata") != j.end())
     {
         j.at("additionalMetadata").get_to(o.m_AdditionalMetadata);
         o.m_AdditionalMetadataIsSet = true;
     } 
-    if(j.contains("file"))
+    if(j.find("file") != j.end())
     {
         j.at("file").get_to(o.m_file);
         o.m_fileIsSet = true;
diff --git a/samples/server/petstore/cpp-pistache/model/Order.cpp b/samples/server/petstore/cpp-pistache/model/Order.cpp
index b24cc0fce92..82efbce6cb2 100644
--- a/samples/server/petstore/cpp-pistache/model/Order.cpp
+++ b/samples/server/petstore/cpp-pistache/model/Order.cpp
@@ -63,32 +63,32 @@ void to_json(nlohmann::json& j, const Order& o)
 
 void from_json(const nlohmann::json& j, Order& o)
 {
-    if(j.contains("id"))
+    if(j.find("id") != j.end())
     {
         j.at("id").get_to(o.m_Id);
         o.m_IdIsSet = true;
     } 
-    if(j.contains("petId"))
+    if(j.find("petId") != j.end())
     {
         j.at("petId").get_to(o.m_PetId);
         o.m_PetIdIsSet = true;
     } 
-    if(j.contains("quantity"))
+    if(j.find("quantity") != j.end())
     {
         j.at("quantity").get_to(o.m_Quantity);
         o.m_QuantityIsSet = true;
     } 
-    if(j.contains("shipDate"))
+    if(j.find("shipDate") != j.end())
     {
         j.at("shipDate").get_to(o.m_ShipDate);
         o.m_ShipDateIsSet = true;
     } 
-    if(j.contains("status"))
+    if(j.find("status") != j.end())
     {
         j.at("status").get_to(o.m_Status);
         o.m_StatusIsSet = true;
     } 
-    if(j.contains("complete"))
+    if(j.find("complete") != j.end())
     {
         j.at("complete").get_to(o.m_Complete);
         o.m_CompleteIsSet = true;
diff --git a/samples/server/petstore/cpp-pistache/model/Pet.cpp b/samples/server/petstore/cpp-pistache/model/Pet.cpp
index 7781e283ceb..1bceb861ad4 100644
--- a/samples/server/petstore/cpp-pistache/model/Pet.cpp
+++ b/samples/server/petstore/cpp-pistache/model/Pet.cpp
@@ -56,24 +56,24 @@ void to_json(nlohmann::json& j, const Pet& o)
 
 void from_json(const nlohmann::json& j, Pet& o)
 {
-    if(j.contains("id"))
+    if(j.find("id") != j.end())
     {
         j.at("id").get_to(o.m_Id);
         o.m_IdIsSet = true;
     } 
-    if(j.contains("category"))
+    if(j.find("category") != j.end())
     {
         j.at("category").get_to(o.m_Category);
         o.m_CategoryIsSet = true;
     } 
     j.at("name").get_to(o.m_Name);
     j.at("photoUrls").get_to(o.m_PhotoUrls);
-    if(j.contains("tags"))
+    if(j.find("tags") != j.end())
     {
         j.at("tags").get_to(o.m_Tags);
         o.m_TagsIsSet = true;
     } 
-    if(j.contains("status"))
+    if(j.find("status") != j.end())
     {
         j.at("status").get_to(o.m_Status);
         o.m_StatusIsSet = true;
diff --git a/samples/server/petstore/cpp-pistache/model/Tag.cpp b/samples/server/petstore/cpp-pistache/model/Tag.cpp
index b81cb825724..7f56fb2bcca 100644
--- a/samples/server/petstore/cpp-pistache/model/Tag.cpp
+++ b/samples/server/petstore/cpp-pistache/model/Tag.cpp
@@ -47,12 +47,12 @@ void to_json(nlohmann::json& j, const Tag& o)
 
 void from_json(const nlohmann::json& j, Tag& o)
 {
-    if(j.contains("id"))
+    if(j.find("id") != j.end())
     {
         j.at("id").get_to(o.m_Id);
         o.m_IdIsSet = true;
     } 
-    if(j.contains("name"))
+    if(j.find("name") != j.end())
     {
         j.at("name").get_to(o.m_Name);
         o.m_NameIsSet = true;
diff --git a/samples/server/petstore/cpp-pistache/model/User.cpp b/samples/server/petstore/cpp-pistache/model/User.cpp
index 66a026e9c78..20ae06352f2 100644
--- a/samples/server/petstore/cpp-pistache/model/User.cpp
+++ b/samples/server/petstore/cpp-pistache/model/User.cpp
@@ -71,42 +71,42 @@ void to_json(nlohmann::json& j, const User& o)
 
 void from_json(const nlohmann::json& j, User& o)
 {
-    if(j.contains("id"))
+    if(j.find("id") != j.end())
     {
         j.at("id").get_to(o.m_Id);
         o.m_IdIsSet = true;
     } 
-    if(j.contains("username"))
+    if(j.find("username") != j.end())
     {
         j.at("username").get_to(o.m_Username);
         o.m_UsernameIsSet = true;
     } 
-    if(j.contains("firstName"))
+    if(j.find("firstName") != j.end())
     {
         j.at("firstName").get_to(o.m_FirstName);
         o.m_FirstNameIsSet = true;
     } 
-    if(j.contains("lastName"))
+    if(j.find("lastName") != j.end())
     {
         j.at("lastName").get_to(o.m_LastName);
         o.m_LastNameIsSet = true;
     } 
-    if(j.contains("email"))
+    if(j.find("email") != j.end())
     {
         j.at("email").get_to(o.m_Email);
         o.m_EmailIsSet = true;
     } 
-    if(j.contains("password"))
+    if(j.find("password") != j.end())
     {
         j.at("password").get_to(o.m_Password);
         o.m_PasswordIsSet = true;
     } 
-    if(j.contains("phone"))
+    if(j.find("phone") != j.end())
     {
         j.at("phone").get_to(o.m_Phone);
         o.m_PhoneIsSet = true;
     } 
-    if(j.contains("userStatus"))
+    if(j.find("userStatus") != j.end())
     {
         j.at("userStatus").get_to(o.m_UserStatus);
         o.m_UserStatusIsSet = true;