diff --git a/modules/openapi-generator/src/main/resources/aspnetcore/3.0/model.mustache b/modules/openapi-generator/src/main/resources/aspnetcore/3.0/model.mustache
index 915d0a58be6..a9e04767cdc 100644
--- a/modules/openapi-generator/src/main/resources/aspnetcore/3.0/model.mustache
+++ b/modules/openapi-generator/src/main/resources/aspnetcore/3.0/model.mustache
@@ -77,7 +77,7 @@ namespace {{modelPackage}}
         public {{{datatypeWithEnum}}}{{#isNullable}}?{{/isNullable}} {{name}} { get; set; }{{#defaultValue}} = {{{.}}};{{/defaultValue}}
         {{/isEnum}}
         {{^isEnum}}
-        public {{{dataType}}} {{name}} { get; set; }{{#defaultValue}} = {{{.}}};{{/defaultValue}}
+        public {{{dataType}}}{{#nullableReferenceTypes}}{{^isContainer}}{{^required}}?{{/required}}{{/isContainer}}{{/nullableReferenceTypes}} {{name}} { get; set; }{{#defaultValue}} = {{{.}}};{{/defaultValue}}
         {{/isEnum}}
         {{^-last}}
 
diff --git a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Animal.cs b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Animal.cs
index 4b04346e358..c9da013dc71 100644
--- a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Animal.cs
+++ b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Animal.cs
@@ -45,7 +45,7 @@ namespace Org.OpenAPITools.Models
         /// Gets or Sets Color
         /// </summary>
         [DataMember(Name="color", EmitDefaultValue=false)]
-        public string Color { get; set; } = "red";
+        public string? Color { get; set; } = "red";
 
         /// <summary>
         /// Returns the string presentation of the object
diff --git a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/ApiResponse.cs b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/ApiResponse.cs
index 2358b07fa7d..638c1313710 100644
--- a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/ApiResponse.cs
+++ b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/ApiResponse.cs
@@ -30,19 +30,19 @@ namespace Org.OpenAPITools.Models
         /// Gets or Sets Code
         /// </summary>
         [DataMember(Name="code", EmitDefaultValue=true)]
-        public int Code { get; set; }
+        public int? Code { get; set; }
 
         /// <summary>
         /// Gets or Sets Type
         /// </summary>
         [DataMember(Name="type", EmitDefaultValue=false)]
-        public string Type { get; set; }
+        public string? Type { get; set; }
 
         /// <summary>
         /// Gets or Sets Message
         /// </summary>
         [DataMember(Name="message", EmitDefaultValue=false)]
-        public string Message { get; set; }
+        public string? Message { get; set; }
 
         /// <summary>
         /// Returns the string presentation of the object
diff --git a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Cat.cs b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Cat.cs
index ef5b1be3efb..710b6a34d82 100644
--- a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Cat.cs
+++ b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Cat.cs
@@ -30,7 +30,7 @@ namespace Org.OpenAPITools.Models
         /// Gets or Sets Declawed
         /// </summary>
         [DataMember(Name="declawed", EmitDefaultValue=true)]
-        public bool Declawed { get; set; }
+        public bool? Declawed { get; set; }
 
         /// <summary>
         /// Returns the string presentation of the object
diff --git a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Category.cs b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Category.cs
index 7898abbb9ff..e9718bd5ca0 100644
--- a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Category.cs
+++ b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Category.cs
@@ -30,14 +30,14 @@ namespace Org.OpenAPITools.Models
         /// Gets or Sets Id
         /// </summary>
         [DataMember(Name="id", EmitDefaultValue=true)]
-        public long Id { get; set; }
+        public long? Id { get; set; }
 
         /// <summary>
         /// Gets or Sets Name
         /// </summary>
         [RegularExpression("^[a-zA-Z0-9]+[a-zA-Z0-9\\.\\-_]*[a-zA-Z0-9]+$")]
         [DataMember(Name="name", EmitDefaultValue=false)]
-        public string Name { get; set; }
+        public string? Name { get; set; }
 
         /// <summary>
         /// Returns the string presentation of the object
diff --git a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Dog.cs b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Dog.cs
index 2dd6a7f4362..5ea23a2f881 100644
--- a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Dog.cs
+++ b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Dog.cs
@@ -30,7 +30,7 @@ namespace Org.OpenAPITools.Models
         /// Gets or Sets Breed
         /// </summary>
         [DataMember(Name="breed", EmitDefaultValue=false)]
-        public string Breed { get; set; }
+        public string? Breed { get; set; }
 
         /// <summary>
         /// Returns the string presentation of the object
diff --git a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Order.cs b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Order.cs
index 5da36e6f1fd..9c63ce71286 100644
--- a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Order.cs
+++ b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Order.cs
@@ -30,25 +30,25 @@ namespace Org.OpenAPITools.Models
         /// Gets or Sets Id
         /// </summary>
         [DataMember(Name="id", EmitDefaultValue=true)]
-        public long Id { get; set; }
+        public long? Id { get; set; }
 
         /// <summary>
         /// Gets or Sets PetId
         /// </summary>
         [DataMember(Name="petId", EmitDefaultValue=true)]
-        public long PetId { get; set; }
+        public long? PetId { get; set; }
 
         /// <summary>
         /// Gets or Sets Quantity
         /// </summary>
         [DataMember(Name="quantity", EmitDefaultValue=true)]
-        public int Quantity { get; set; }
+        public int? Quantity { get; set; }
 
         /// <summary>
         /// Gets or Sets ShipDate
         /// </summary>
         [DataMember(Name="shipDate", EmitDefaultValue=false)]
-        public DateTime ShipDate { get; set; }
+        public DateTime? ShipDate { get; set; }
 
 
         /// <summary>
@@ -90,7 +90,7 @@ namespace Org.OpenAPITools.Models
         /// Gets or Sets Complete
         /// </summary>
         [DataMember(Name="complete", EmitDefaultValue=true)]
-        public bool Complete { get; set; } = false;
+        public bool? Complete { get; set; } = false;
 
         /// <summary>
         /// Returns the string presentation of the object
diff --git a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Pet.cs b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Pet.cs
index 31a57ea7735..69a963a25f2 100644
--- a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Pet.cs
+++ b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Pet.cs
@@ -30,13 +30,13 @@ namespace Org.OpenAPITools.Models
         /// Gets or Sets Id
         /// </summary>
         [DataMember(Name="id", EmitDefaultValue=true)]
-        public long Id { get; set; }
+        public long? Id { get; set; }
 
         /// <summary>
         /// Gets or Sets Category
         /// </summary>
         [DataMember(Name="category", EmitDefaultValue=false)]
-        public Category Category { get; set; }
+        public Category? Category { get; set; }
 
         /// <summary>
         /// Gets or Sets Name
diff --git a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Tag.cs b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Tag.cs
index 84ccb02359b..4d7834b4c52 100644
--- a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Tag.cs
+++ b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/Tag.cs
@@ -30,13 +30,13 @@ namespace Org.OpenAPITools.Models
         /// Gets or Sets Id
         /// </summary>
         [DataMember(Name="id", EmitDefaultValue=true)]
-        public long Id { get; set; }
+        public long? Id { get; set; }
 
         /// <summary>
         /// Gets or Sets Name
         /// </summary>
         [DataMember(Name="name", EmitDefaultValue=false)]
-        public string Name { get; set; }
+        public string? Name { get; set; }
 
         /// <summary>
         /// Returns the string presentation of the object
diff --git a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/User.cs b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/User.cs
index 9155e7309fc..4d07fc1ef74 100644
--- a/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/User.cs
+++ b/samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Models/User.cs
@@ -30,50 +30,50 @@ namespace Org.OpenAPITools.Models
         /// Gets or Sets Id
         /// </summary>
         [DataMember(Name="id", EmitDefaultValue=true)]
-        public long Id { get; set; }
+        public long? Id { get; set; }
 
         /// <summary>
         /// Gets or Sets Username
         /// </summary>
         [DataMember(Name="username", EmitDefaultValue=false)]
-        public string Username { get; set; }
+        public string? Username { get; set; }
 
         /// <summary>
         /// Gets or Sets FirstName
         /// </summary>
         [DataMember(Name="firstName", EmitDefaultValue=false)]
-        public string FirstName { get; set; }
+        public string? FirstName { get; set; }
 
         /// <summary>
         /// Gets or Sets LastName
         /// </summary>
         [DataMember(Name="lastName", EmitDefaultValue=false)]
-        public string LastName { get; set; }
+        public string? LastName { get; set; }
 
         /// <summary>
         /// Gets or Sets Email
         /// </summary>
         [DataMember(Name="email", EmitDefaultValue=false)]
-        public string Email { get; set; }
+        public string? Email { get; set; }
 
         /// <summary>
         /// Gets or Sets Password
         /// </summary>
         [DataMember(Name="password", EmitDefaultValue=false)]
-        public string Password { get; set; }
+        public string? Password { get; set; }
 
         /// <summary>
         /// Gets or Sets Phone
         /// </summary>
         [DataMember(Name="phone", EmitDefaultValue=false)]
-        public string Phone { get; set; }
+        public string? Phone { get; set; }
 
         /// <summary>
         /// User Status
         /// </summary>
         /// <value>User Status</value>
         [DataMember(Name="userStatus", EmitDefaultValue=true)]
-        public int UserStatus { get; set; }
+        public int? UserStatus { get; set; }
 
         /// <summary>
         /// Returns the string presentation of the object