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 fcdd9df869bc..241b3f881ef0 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
@@ -2924,7 +2924,7 @@ protected void updateModelForComposedSchema(CodegenModel m, Schema schema, Map<S
             addAdditionPropertiesToCodeGenModel(m, schema);
         }
 
-        if (Boolean.TRUE.equals(schema.getNullable())) {
+        if (ModelUtils.isNullable(schema)) {
             m.isNullable = Boolean.TRUE;
         }
 
@@ -3926,8 +3926,6 @@ public CodegenProperty fromProperty(String name, Schema p, boolean required, boo
         }
         if (ModelUtils.isNullable(p)) {
             property.isNullable = true;
-        } else if (p.getNullable() != null) {
-            property.isNullable = p.getNullable();
         }
 
         if (p.getExtensions() != null && !p.getExtensions().isEmpty()) {
@@ -3977,14 +3975,8 @@ public CodegenProperty fromProperty(String name, Schema p, boolean required, boo
             }
         }
 
-        // set isNullable using nullable or x-nullable in the schema
         if (ModelUtils.isNullable(referencedSchema)) {
             property.isNullable = true;
-        } else if (referencedSchema.getNullable() != null) {
-            property.isNullable = referencedSchema.getNullable();
-        } else if (referencedSchema.getExtensions() != null &&
-                referencedSchema.getExtensions().containsKey(X_NULLABLE)) {
-            property.isNullable = (Boolean) referencedSchema.getExtensions().get(X_NULLABLE);
         }
 
         final XML referencedSchemaXml = referencedSchema.getXml();
@@ -4085,10 +4077,6 @@ public CodegenProperty fromProperty(String name, Schema p, boolean required, boo
             // evaluate common attributes if defined in the top level
             if (ModelUtils.isNullable(p)) {
                 property.isNullable = true;
-            } else if (p.getNullable() != null) {
-                property.isNullable = p.getNullable();
-            } else if (p.getExtensions() != null && p.getExtensions().containsKey(X_NULLABLE)) {
-                property.isNullable = (Boolean) p.getExtensions().get(X_NULLABLE);
             }
 
             if (p.getReadOnly() != null) {
@@ -5292,7 +5280,7 @@ public CodegenParameter fromParameter(Parameter parameter, Set<String> imports)
         codegenParameter.setTypeProperties(parameterSchema, openAPI);
         codegenParameter.setComposedSchemas(getComposedSchemas(parameterSchema));
 
-        if (Boolean.TRUE.equals(parameterSchema.getNullable())) { // use nullable defined in the spec
+        if (ModelUtils.isNullable(parameterSchema)) { // use nullable defined in the spec
             codegenParameter.isNullable = true;
         }
 
@@ -8066,7 +8054,9 @@ public CodegenParameter fromRequestBody(RequestBody body, Set<String> imports, S
             if (original.getNullable() != null) {
                 codegenParameter.isNullable = original.getNullable();
             } else if (original.getExtensions() != null && original.getExtensions().containsKey(X_NULLABLE)) {
-                codegenParameter.isNullable = (Boolean) original.getExtensions().get(X_NULLABLE);
+                codegenParameter.isNullable = Boolean.parseBoolean(String.valueOf(original.getExtensions().get(X_NULLABLE)));
+            } else if (ModelUtils.isNullable(original)) {
+                codegenParameter.isNullable = true;
             }
 
             if (original.getExtensions() != null) {
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/OpenAPINormalizer.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/OpenAPINormalizer.java
index 9a304b529503..d0b71a23d1c3 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/OpenAPINormalizer.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/OpenAPINormalizer.java
@@ -998,8 +998,8 @@ public Schema normalizeSchema(Schema schema, Set<Schema> visitedSchemas) {
             }
             normalizeProperties(schema, visitedSchemas);
         } else if (schema.getAdditionalProperties() instanceof Schema) { // map
-            normalizeMapSchema(schema);
-            Schema additionalProperties = (Schema) schema.getAdditionalProperties();
+            Schema result = normalizeMapSchema(schema);
+            Schema additionalProperties = (Schema) result.getAdditionalProperties();
             if (getRule(NORMALIZE_31SPEC) && ModelUtils.isNullTypeSchema(openAPI, additionalProperties)) {
                 // OAS 3.1 allows a map value schema of `type: "null"` (e.g.
                 // `additionalProperties: { type: "null" }`). There's no OAS 3.0 equivalent type,
@@ -1008,15 +1008,17 @@ public Schema normalizeSchema(Schema schema, Set<Schema> visitedSchemas) {
                 // generated as a normal (nullable) object instead.
                 Schema anyTypeNullable = new Schema();
                 anyTypeNullable.setNullable(true);
-                schema.setAdditionalProperties(anyTypeNullable);
+                result.setAdditionalProperties(anyTypeNullable);
             } else {
                 Schema normalized = normalizeSchema(additionalProperties, visitedSchemas);
                 if (getRule(NORMALIZE_31SPEC)) {
                     // capture the normalized value schema (e.g. an OAS 3.1 `type: [array, "null"]`
                     // value is rewritten to a proper array schema), which would otherwise be lost.
-                    schema.setAdditionalProperties(normalized);
+                    result.setAdditionalProperties(normalized);
                 }
             }
+
+            return result;
         } else if (schema instanceof BooleanSchema) {
             normalizeBooleanSchema(schema, visitedSchemas);
         } else if (schema instanceof IntegerSchema) {
@@ -1105,7 +1107,8 @@ protected Schema normalizeArraySchema(Schema schema) {
     }
 
     protected Schema normalizeMapSchema(Schema schema) {
-        return processSetMapToNullable(schema);
+        Schema result = processNormalize31Spec(schema, new HashSet<>());
+        return processSetMapToNullable(result);
     }
 
     protected Schema normalizeSimpleSchema(Schema schema, Set<Schema> visitedSchemas) {
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/ModelUtils.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/ModelUtils.java
index 01221e7cc26c..40058b1e90f2 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/ModelUtils.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/ModelUtils.java
@@ -2001,9 +2001,7 @@ public static boolean isNullable(Schema schema) {
         if (schema.getExtensions() != null && schema.getExtensions().get(X_NULLABLE) != null) {
             return Boolean.parseBoolean(schema.getExtensions().get(X_NULLABLE).toString());
         }
-        if (schema.getTypes() != null && schema.getTypes().contains("null")) {
-            return true;
-        }
+
         // In OAS 3.1, the recommended way to define a nullable property or object is to use oneOf.
         if (isComposedSchema(schema)) {
             return isNullableComposedSchema(schema);
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/validations/oas/OpenApiSchemaValidationsTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/validations/oas/OpenApiSchemaValidationsTest.java
index e71005f794c2..a48d714d88a5 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/validations/oas/OpenApiSchemaValidationsTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/validations/oas/OpenApiSchemaValidationsTest.java
@@ -96,7 +96,7 @@ public void testNullableAttributeInOas31_triggerWarning() {
     /**
      * The nullable-deprecated warning must NOT fire for an OAS 3.1 spec using the correct 3.1 null type syntax.
      */
-    @Test(enabled = false, description = "correct OAS 3.1 null type syntax (type: [string, null]) must NOT trigger the nullable-deprecated warning")
+    @Test(description = "correct OAS 3.1 null type syntax (type: [string, null]) must NOT trigger the nullable-deprecated warning")
     public void testNullTypeInOas31_noWarning() {
         OpenAPI openAPI = TestUtils.parseSpec("src/test/resources/3_1/null-types-simple.yaml");
         Schema<?> stringDataOrNull = (Schema<?>) openAPI.getComponents().getSchemas().get("WithNullableType").getProperties().get("stringDataOrNull");
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 4348ded2a682..6c8d12078e36 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
@@ -325,6 +325,7 @@ paths:
                 additionalProperties:
                   format: int32
                   type: integer
+                type: object
           description: successful operation
       security:
       - api_key: []