diff --git a/modules/openapi-generator/src/test/resources/3_1/java/petstore.yaml b/modules/openapi-generator/src/test/resources/3_1/java/petstore.yaml
index 0b5d6425f40e..704dc12186d9 100644
--- a/modules/openapi-generator/src/test/resources/3_1/java/petstore.yaml
+++ b/modules/openapi-generator/src/test/resources/3_1/java/petstore.yaml
@@ -1125,3 +1125,6 @@ components:
             - "object"
             - "null"
           $ref: '#/components/schemas/Pet'
+        second_property:
+          description: just null type
+          type: null
diff --git a/samples/client/petstore/java/okhttp-gson-3.1/api/openapi.yaml b/samples/client/petstore/java/okhttp-gson-3.1/api/openapi.yaml
index 6c8d12078e36..45d0e4167627 100644
--- a/samples/client/petstore/java/okhttp-gson-3.1/api/openapi.yaml
+++ b/samples/client/petstore/java/okhttp-gson-3.1/api/openapi.yaml
@@ -1204,6 +1204,8 @@ components:
       properties:
         first_property:
           $ref: "#/components/schemas/Pet"
+        second_property:
+          description: just null type
     updatePetWithForm_request:
       properties:
         name:
diff --git a/samples/client/petstore/java/okhttp-gson-3.1/docs/PetWithTypesObjectNullAndRef.md b/samples/client/petstore/java/okhttp-gson-3.1/docs/PetWithTypesObjectNullAndRef.md
index 618d36cc0b19..f2554b172d33 100644
--- a/samples/client/petstore/java/okhttp-gson-3.1/docs/PetWithTypesObjectNullAndRef.md
+++ b/samples/client/petstore/java/okhttp-gson-3.1/docs/PetWithTypesObjectNullAndRef.md
@@ -8,6 +8,7 @@
 | Name | Type | Description | Notes |
 |------------ | ------------- | ------------- | -------------|
 |**firstProperty** | [**Pet**](Pet.md) |  |  [optional] |
+|**secondProperty** | **Object** | just null type |  [optional] |
 
 
 
diff --git a/samples/client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/PetWithTypesObjectNullAndRef.java b/samples/client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/PetWithTypesObjectNullAndRef.java
index 1fcc9f858e46..4b0e53dc8bce 100644
--- a/samples/client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/PetWithTypesObjectNullAndRef.java
+++ b/samples/client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/PetWithTypesObjectNullAndRef.java
@@ -22,6 +22,7 @@
 import java.io.IOException;
 import java.util.Arrays;
 import org.openapitools.client.model.Pet;
+import org.openapitools.jackson.nullable.JsonNullable;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
@@ -57,6 +58,11 @@ public class PetWithTypesObjectNullAndRef {
   @javax.annotation.Nullable
   private Pet firstProperty;
 
+  public static final String SERIALIZED_NAME_SECOND_PROPERTY = "second_property";
+  @SerializedName(SERIALIZED_NAME_SECOND_PROPERTY)
+  @javax.annotation.Nullable
+  private Object secondProperty = null;
+
   public PetWithTypesObjectNullAndRef() {
   }
 
@@ -78,6 +84,25 @@ public void setFirstProperty(@javax.annotation.Nullable Pet firstProperty) {
     this.firstProperty = firstProperty;
   }
 
+
+  public PetWithTypesObjectNullAndRef secondProperty(@javax.annotation.Nullable Object secondProperty) {
+    this.secondProperty = secondProperty;
+    return this;
+  }
+
+  /**
+   * just null type
+   * @return secondProperty
+   */
+  @javax.annotation.Nullable
+  public Object getSecondProperty() {
+    return secondProperty;
+  }
+
+  public void setSecondProperty(@javax.annotation.Nullable Object secondProperty) {
+    this.secondProperty = secondProperty;
+  }
+
   /**
    * A container for additional, undeclared properties.
    * This is a holder for any undeclared properties as specified with
@@ -133,13 +158,25 @@ public boolean equals(Object o) {
       return false;
     }
     PetWithTypesObjectNullAndRef petWithTypesObjectNullAndRef = (PetWithTypesObjectNullAndRef) o;
-    return Objects.equals(this.firstProperty, petWithTypesObjectNullAndRef.firstProperty)&&
+    return Objects.equals(this.firstProperty, petWithTypesObjectNullAndRef.firstProperty) &&
+        Objects.equals(this.secondProperty, petWithTypesObjectNullAndRef.secondProperty)&&
         Objects.equals(this.additionalProperties, petWithTypesObjectNullAndRef.additionalProperties);
   }
 
+  private static <T> boolean equalsNullable(JsonNullable<T> a, JsonNullable<T> b) {
+    return a == b || (a != null && b != null && a.isPresent() && b.isPresent() && Objects.deepEquals(a.get(), b.get()));
+  }
+
   @Override
   public int hashCode() {
-    return Objects.hash(firstProperty, additionalProperties);
+    return Objects.hash(firstProperty, secondProperty, additionalProperties);
+  }
+
+  private static <T> int hashCodeNullable(JsonNullable<T> a) {
+    if (a == null) {
+      return 1;
+    }
+    return a.isPresent() ? Arrays.deepHashCode(new Object[]{a.get()}) : 31;
   }
 
   @Override
@@ -147,6 +184,7 @@ public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append("class PetWithTypesObjectNullAndRef {\n");
     sb.append("    firstProperty: ").append(toIndentedString(firstProperty)).append("\n");
+    sb.append("    secondProperty: ").append(toIndentedString(secondProperty)).append("\n");
     sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
@@ -166,7 +204,7 @@ private String toIndentedString(Object o) {
 
   static {
     // a set of all properties/fields (JSON key names)
-    openapiFields = new HashSet<String>(Arrays.asList("first_property"));
+    openapiFields = new HashSet<String>(Arrays.asList("first_property", "second_property"));
 
     // a set of required properties/fields (JSON key names)
     openapiRequiredFields = new HashSet<String>(0);