diff --git a/modules/openapi-generator/src/main/resources/dart2/serialization/native/native_class.mustache b/modules/openapi-generator/src/main/resources/dart2/serialization/native/native_class.mustache
index 07c0b5b9b411..01462d445a11 100644
--- a/modules/openapi-generator/src/main/resources/dart2/serialization/native/native_class.mustache
+++ b/modules/openapi-generator/src/main/resources/dart2/serialization/native/native_class.mustache
@@ -195,6 +195,19 @@ class {{{classname}}} {
         {{#complexType}}
           {{#isArray}}
             {{#items.isArray}}
+              {{#vendorExtensions.x-is-optional}}
+        {{{name}}}: json.containsKey(r'{{{baseName}}}') ? Optional.present(json[r'{{{baseName}}}'] is List
+          ? (json[r'{{{baseName}}}'] as List).map((e) =>
+              {{#items.complexType}}
+              e == null ? {{#items.isNullable}}null{{/items.isNullable}}{{^items.isNullable}}const <{{items.complexType}}>[]{{/items.isNullable}} : {{items.complexType}}.listFromJson(e){{#uniqueItems}}.toSet(){{/uniqueItems}}
+              {{/items.complexType}}
+              {{^items.complexType}}
+              e == null ? {{#items.isNullable}}null{{/items.isNullable}}{{^items.isNullable}}const <{{items.items.dataType}}{{#items.items.isNullable}}?{{/items.items.isNullable}}>[]{{/items.isNullable}} : (e as List).map((value) => value as {{items.items.dataType}}{{#items.items.isNullable}}?{{/items.items.isNullable}}).toList(growable: false)
+              {{/items.complexType}}
+            ).toList()
+          :  {{#isNullable}}null{{/isNullable}}{{^isNullable}}const []{{/isNullable}}) : const Optional.absent(),
+              {{/vendorExtensions.x-is-optional}}
+              {{^vendorExtensions.x-is-optional}}
         {{{name}}}: json[r'{{{baseName}}}'] is List
           ? (json[r'{{{baseName}}}'] as List).map((e) =>
               {{#items.complexType}}
@@ -205,38 +218,75 @@ class {{{classname}}} {
               {{/items.complexType}}
             ).toList()
           :  {{#isNullable}}null{{/isNullable}}{{^isNullable}}const []{{/isNullable}},
+              {{/vendorExtensions.x-is-optional}}
             {{/items.isArray}}
             {{^items.isArray}}
+              {{#vendorExtensions.x-is-optional}}
+        {{{name}}}: json.containsKey(r'{{{baseName}}}') ? Optional.present({{{complexType}}}.listFromJson(json[r'{{{baseName}}}']){{#uniqueItems}}.toSet(){{/uniqueItems}}) : const Optional.absent(),
+              {{/vendorExtensions.x-is-optional}}
+              {{^vendorExtensions.x-is-optional}}
         {{{name}}}: {{{complexType}}}.listFromJson(json[r'{{{baseName}}}']){{#uniqueItems}}.toSet(){{/uniqueItems}},
+              {{/vendorExtensions.x-is-optional}}
             {{/items.isArray}}
           {{/isArray}}
           {{^isArray}}
             {{#isMap}}
               {{#items.isArray}}
+                {{#vendorExtensions.x-is-optional}}
+        {{{name}}}: json.containsKey(r'{{{baseName}}}') ? Optional.present(json[r'{{{baseName}}}'] == null ? null
+                  {{#items.complexType}}
+            : {{items.complexType}}.mapListFromJson(json[r'{{{baseName}}}'])) : const Optional.absent(),
+                  {{/items.complexType}}
+                  {{^items.complexType}}
+            : (json[r'{{{baseName}}}'] as Map<String, dynamic>).map((k, v) => MapEntry(k, v == null ? {{#items.isNullable}}null{{/items.isNullable}}{{^items.isNullable}}const <{{items.items.dataType}}{{#items.items.isNullable}}?{{/items.items.isNullable}}>[]{{/items.isNullable}} : (v as List).map((value) => value as {{items.items.dataType}}{{#items.items.isNullable}}?{{/items.items.isNullable}}).toList(growable: false)))) : const Optional.absent(),
+                  {{/items.complexType}}
+                {{/vendorExtensions.x-is-optional}}
+                {{^vendorExtensions.x-is-optional}}
         {{{name}}}: json[r'{{{baseName}}}'] == null
           ? {{#defaultValue}}{{{.}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}}
-                {{#items.complexType}}
+                  {{#items.complexType}}
             : {{items.complexType}}.mapListFromJson(json[r'{{{baseName}}}']),
-                {{/items.complexType}}
-                {{^items.complexType}}
+                  {{/items.complexType}}
+                  {{^items.complexType}}
             : (json[r'{{{baseName}}}'] as Map<String, dynamic>).map((k, v) => MapEntry(k, v == null ? {{#items.isNullable}}null{{/items.isNullable}}{{^items.isNullable}}const <{{items.items.dataType}}{{#items.items.isNullable}}?{{/items.items.isNullable}}>[]{{/items.isNullable}} : (v as List).map((value) => value as {{items.items.dataType}}{{#items.items.isNullable}}?{{/items.items.isNullable}}).toList(growable: false))),
-                {{/items.complexType}}
+                  {{/items.complexType}}
+                {{/vendorExtensions.x-is-optional}}
               {{/items.isArray}}
               {{^items.isArray}}
                 {{#items.isMap}}
                   {{#items.complexType}}
+                    {{#vendorExtensions.x-is-optional}}
+        {{{name}}}: json.containsKey(r'{{{baseName}}}') ? Optional.present({{items.complexType}}.mapFromJson(json[r'{{{baseName}}}'])) : const Optional.absent(),
+                    {{/vendorExtensions.x-is-optional}}
+                    {{^vendorExtensions.x-is-optional}}
         {{{name}}}: {{items.complexType}}.mapFromJson(json[r'{{{baseName}}}']),
+                    {{/vendorExtensions.x-is-optional}}
                   {{/items.complexType}}
                   {{^items.complexType}}
+                    {{#vendorExtensions.x-is-optional}}
+        {{{name}}}: json.containsKey(r'{{{baseName}}}') ? Optional.present(mapCastOfType<String, dynamic>(json, r'{{{baseName}}}')) : const Optional.absent(),
+                    {{/vendorExtensions.x-is-optional}}
+                    {{^vendorExtensions.x-is-optional}}
         {{{name}}}: mapCastOfType<String, dynamic>(json, r'{{{baseName}}}'){{#required}}{{^isNullable}}!{{/isNullable}}{{/required}}{{^required}}{{#defaultValue}} ?? {{{.}}}{{/defaultValue}}{{/required}},
+                    {{/vendorExtensions.x-is-optional}}
                   {{/items.complexType}}
                 {{/items.isMap}}
                 {{^items.isMap}}
                   {{#items.complexType}}
+                    {{#vendorExtensions.x-is-optional}}
+        {{{name}}}: json.containsKey(r'{{{baseName}}}') ? Optional.present({{{items.complexType}}}.mapFromJson(json[r'{{{baseName}}}'])) : const Optional.absent(),
+                    {{/vendorExtensions.x-is-optional}}
+                    {{^vendorExtensions.x-is-optional}}
         {{{name}}}: {{{items.complexType}}}.mapFromJson(json[r'{{{baseName}}}']),
+                    {{/vendorExtensions.x-is-optional}}
                   {{/items.complexType}}
                   {{^items.complexType}}
+                    {{#vendorExtensions.x-is-optional}}
+        {{{name}}}: json.containsKey(r'{{{baseName}}}') ? Optional.present(mapCastOfType<String, {{items.dataType}}>(json, r'{{{baseName}}}')) : const Optional.absent(),
+                    {{/vendorExtensions.x-is-optional}}
+                    {{^vendorExtensions.x-is-optional}}
         {{{name}}}: mapCastOfType<String, {{items.dataType}}>(json, r'{{{baseName}}}'){{#required}}{{^isNullable}}!{{/isNullable}}{{/required}}{{^required}}{{#defaultValue}} ?? {{{.}}}{{/defaultValue}}{{/required}},
+                    {{/vendorExtensions.x-is-optional}}
                   {{/items.complexType}}
                 {{/items.isMap}}
               {{/items.isArray}}
@@ -259,23 +309,45 @@ class {{{classname}}} {
         {{^complexType}}
           {{#isArray}}
             {{#isEnum}}
+              {{#vendorExtensions.x-is-optional}}
+        {{{name}}}: json.containsKey(r'{{{baseName}}}') ? Optional.present({{{items.datatypeWithEnum}}}.listFromJson(json[r'{{{baseName}}}']){{#uniqueItems}}.toSet(){{/uniqueItems}}) : const Optional.absent(),
+              {{/vendorExtensions.x-is-optional}}
+              {{^vendorExtensions.x-is-optional}}
         {{{name}}}: {{{items.datatypeWithEnum}}}.listFromJson(json[r'{{{baseName}}}']){{#uniqueItems}}.toSet(){{/uniqueItems}},
+              {{/vendorExtensions.x-is-optional}}
             {{/isEnum}}
             {{^isEnum}}
+              {{#vendorExtensions.x-is-optional}}
+        {{{name}}}: json.containsKey(r'{{{baseName}}}') ? Optional.present(json[r'{{{baseName}}}'] is Iterable
+            ? (json[r'{{{baseName}}}'] as Iterable).cast<{{{items.datatype}}}>().{{#uniqueItems}}toSet(){{/uniqueItems}}{{^uniqueItems}}toList(growable: false){{/uniqueItems}}
+            : {{#defaultValue}}{{{.}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}}) : const Optional.absent(),
+              {{/vendorExtensions.x-is-optional}}
+              {{^vendorExtensions.x-is-optional}}
         {{{name}}}: json[r'{{{baseName}}}'] is Iterable
             ? (json[r'{{{baseName}}}'] as Iterable).cast<{{{items.datatype}}}>().{{#uniqueItems}}toSet(){{/uniqueItems}}{{^uniqueItems}}toList(growable: false){{/uniqueItems}}
             : {{#defaultValue}}{{{.}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}},
+              {{/vendorExtensions.x-is-optional}}
             {{/isEnum}}
           {{/isArray}}
           {{^isArray}}
             {{#isMap}}
+              {{#vendorExtensions.x-is-optional}}
+        {{{name}}}: json.containsKey(r'{{{baseName}}}') ? Optional.present(mapCastOfType<String, {{{items.datatype}}}>(json, r'{{{baseName}}}')) : const Optional.absent(),
+              {{/vendorExtensions.x-is-optional}}
+              {{^vendorExtensions.x-is-optional}}
         {{{name}}}: mapCastOfType<String, {{{items.datatype}}}>(json, r'{{{baseName}}}'){{#required}}{{^isNullable}}!{{/isNullable}}{{/required}}{{^required}}{{#defaultValue}} ?? {{{.}}}{{/defaultValue}}{{/required}},
+              {{/vendorExtensions.x-is-optional}}
             {{/isMap}}
             {{^isMap}}
               {{#isNumber}}
+                {{#vendorExtensions.x-is-optional}}
+        {{{name}}}: json.containsKey(r'{{{baseName}}}') ? Optional.present(json[r'{{{baseName}}}'] == null ? null : num.parse('${json[r'{{{baseName}}}']}')) : const Optional.absent(),
+                {{/vendorExtensions.x-is-optional}}
+                {{^vendorExtensions.x-is-optional}}
         {{{name}}}: {{#isNullable}}json[r'{{{baseName}}}'] == null
             ? {{#defaultValue}}{{{.}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}}
             : {{/isNullable}}{{{datatypeWithEnum}}}.parse('${json[r'{{{baseName}}}']}'),
+                {{/vendorExtensions.x-is-optional}}
               {{/isNumber}}
               {{^isNumber}}
                 {{#vendorExtensions.x-original-is-integer}}
diff --git a/modules/openapi-generator/src/test/resources/3_0/kotlin/reserved_words.yaml b/modules/openapi-generator/src/test/resources/3_0/kotlin/reserved_words.yaml
index 38356d3aacda..4c2c3ee996ee 100644
--- a/modules/openapi-generator/src/test/resources/3_0/kotlin/reserved_words.yaml
+++ b/modules/openapi-generator/src/test/resources/3_0/kotlin/reserved_words.yaml
@@ -178,7 +178,7 @@ components:
           type: string
         is:
           type: string
-        null:
+        "null":
           type: string
         object:
           type: string
@@ -251,7 +251,7 @@ components:
           $ref: '#/components/schemas/interface'
         is:
           $ref: '#/components/schemas/is'
-        null:
+        "null":
           $ref: '#/components/schemas/null'
         object:
           $ref: '#/components/schemas/object'
@@ -401,7 +401,7 @@ components:
           type: integer
           format: int64
 
-    null:
+    "null":
       title: Testing reserved word 'null'
       type: object
       properties: