diff --git a/modules/openapi-generator/src/main/resources/dart2/api_helper.mustache b/modules/openapi-generator/src/main/resources/dart2/api_helper.mustache
index ec98b7d1d741..6268a5af3e48 100644
--- a/modules/openapi-generator/src/main/resources/dart2/api_helper.mustache
+++ b/modules/openapi-generator/src/main/resources/dart2/api_helper.mustache
@@ -86,7 +86,7 @@ DateTime? mapDateTime(dynamic map, String key, [String? pattern]) {
     if (value is int) {
       millis = value;
     } else if (value is String) {
-      if (pattern == _dateEpochMarker) {
+      if (_isEpochMarker(pattern)) {
         millis = int.tryParse(value);
       } else {
         return DateTime.tryParse(value);
diff --git a/modules/openapi-generator/src/main/resources/dart2/apilib.mustache b/modules/openapi-generator/src/main/resources/dart2/apilib.mustache
index 2fcebda4ea46..876eba03cc6e 100644
--- a/modules/openapi-generator/src/main/resources/dart2/apilib.mustache
+++ b/modules/openapi-generator/src/main/resources/dart2/apilib.mustache
@@ -31,3 +31,5 @@ final _regSet = RegExp(r'^Set<(.*)>$');
 final _regMap = RegExp(r'^Map<String,(.*)>$');
 
 ApiClient defaultApiClient = ApiClient();
+
+bool _isEpochMarker(String? pattern) => pattern == _dateEpochMarker || pattern == '/$_dateEpochMarker/';
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 a8a6273cf280..6700c86ed1de 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
@@ -66,7 +66,7 @@ class {{{classname}}} {
     {{/isNullable}}
     {{#isDateTime}}
       {{#pattern}}
-      json[r'{{{baseName}}}'] = _dateEpochMarker == '{{{pattern}}}'
+      json[r'{{{baseName}}}'] = _isEpochMarker(r'{{{pattern}}}')
         ? this.{{{name}}}{{#isNullable}}!{{/isNullable}}{{^isNullable}}{{^required}}{{^defaultValue}}!{{/defaultValue}}{{/required}}{{/isNullable}}.millisecondsSinceEpoch
         : this.{{{name}}}{{#isNullable}}!{{/isNullable}}{{^isNullable}}{{^required}}{{^defaultValue}}!{{/defaultValue}}{{/required}}{{/isNullable}}.toUtc().toIso8601String();
       {{/pattern}}
@@ -76,7 +76,7 @@ class {{{classname}}} {
     {{/isDateTime}}
     {{#isDate}}
       {{#pattern}}
-      json[r'{{{baseName}}}'] = _dateEpochMarker == '{{{pattern}}}'
+      json[r'{{{baseName}}}'] = _isEpochMarker(r'{{{pattern}}}')
         ? this.{{{name}}}{{#isNullable}}!{{/isNullable}}{{^isNullable}}{{^required}}{{^defaultValue}}!{{/defaultValue}}{{/required}}{{/isNullable}}.millisecondsSinceEpoch
         : _dateFormatter.format(this.{{{name}}}{{#isNullable}}!{{/isNullable}}{{^isNullable}}{{^required}}{{^defaultValue}}!{{/defaultValue}}{{/required}}{{/isNullable}}.toUtc());
       {{/pattern}}
@@ -128,10 +128,10 @@ class {{{classname}}} {
       return {{{classname}}}(
   {{#vars}}
     {{#isDateTime}}
-        {{{name}}}: mapDateTime(json, r'{{{baseName}}}', '{{{pattern}}}'){{#required}}{{^isNullable}}!{{/isNullable}}{{/required}}{{^required}}{{#defaultValue}} ?? {{{.}}}{{/defaultValue}}{{/required}},
+        {{{name}}}: mapDateTime(json, r'{{{baseName}}}', r'{{{pattern}}}'){{#required}}{{^isNullable}}!{{/isNullable}}{{/required}}{{^required}}{{#defaultValue}} ?? {{{.}}}{{/defaultValue}}{{/required}},
     {{/isDateTime}}
     {{#isDate}}
-        {{{name}}}: mapDateTime(json, r'{{{baseName}}}', '{{{pattern}}}'){{#required}}{{^isNullable}}!{{/isNullable}}{{/required}}{{^required}}{{#defaultValue}} ?? {{{.}}}{{/defaultValue}}{{/required}},
+        {{{name}}}: mapDateTime(json, r'{{{baseName}}}', r'{{{pattern}}}'){{#required}}{{^isNullable}}!{{/isNullable}}{{/required}}{{^required}}{{#defaultValue}} ?? {{{.}}}{{/defaultValue}}{{/required}},
     {{/isDate}}
     {{^isDateTime}}
       {{^isDate}}
@@ -211,9 +211,9 @@ class {{{classname}}} {
             {{/isMap}}
             {{^isMap}}
               {{#isNumber}}
-        {{{name}}}: json[r'{{{baseName}}}'] == null
+        {{{name}}}: {{#isNullable}}json[r'{{{baseName}}}'] == null
             ? {{#defaultValue}}{{{.}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}}
-            : {{{datatypeWithEnum}}}.parse(json[r'{{{baseName}}}'].toString()),
+            : {{/isNullable}}{{{datatypeWithEnum}}}.parse('${json[r'{{{baseName}}}']}'),
               {{/isNumber}}
               {{^isNumber}}
                 {{^isEnum}}
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/api.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/api.dart
index 742bcfa11543..e7da4386a7dd 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/api.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/api.dart
@@ -47,3 +47,5 @@ final _regSet = RegExp(r'^Set<(.*)>$');
 final _regMap = RegExp(r'^Map<String,(.*)>$');
 
 ApiClient defaultApiClient = ApiClient();
+
+bool _isEpochMarker(String? pattern) => pattern == _dateEpochMarker || pattern == '/$_dateEpochMarker/';
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/api_helper.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/api_helper.dart
index d6adb1798250..b0d63582d2f0 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/api_helper.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/api_helper.dart
@@ -87,7 +87,7 @@ DateTime? mapDateTime(dynamic map, String key, [String? pattern]) {
     if (value is int) {
       millis = value;
     } else if (value is String) {
-      if (pattern == _dateEpochMarker) {
+      if (_isEpochMarker(pattern)) {
         millis = int.tryParse(value);
       } else {
         return DateTime.tryParse(value);
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/order.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/order.dart
index 0894d4b295c5..e052dcc544a9 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/order.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/order.dart
@@ -133,7 +133,7 @@ class Order {
         id: mapValueOfType<int>(json, r'id'),
         petId: mapValueOfType<int>(json, r'petId'),
         quantity: mapValueOfType<int>(json, r'quantity'),
-        shipDate: mapDateTime(json, r'shipDate', ''),
+        shipDate: mapDateTime(json, r'shipDate', r''),
         status: OrderStatusEnum.fromJson(json[r'status']),
         complete: mapValueOfType<bool>(json, r'complete') ?? false,
       );
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api.dart
index 78bbb5b3f0de..3354e842e543 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api.dart
@@ -92,3 +92,5 @@ final _regSet = RegExp(r'^Set<(.*)>$');
 final _regMap = RegExp(r'^Map<String,(.*)>$');
 
 ApiClient defaultApiClient = ApiClient();
+
+bool _isEpochMarker(String? pattern) => pattern == _dateEpochMarker || pattern == '/$_dateEpochMarker/';
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api_helper.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api_helper.dart
index 4a29277289d8..77898c911eee 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api_helper.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api_helper.dart
@@ -105,7 +105,7 @@ DateTime? mapDateTime(dynamic map, String key, [String? pattern]) {
     if (value is int) {
       millis = value;
     } else if (value is String) {
-      if (pattern == _dateEpochMarker) {
+      if (_isEpochMarker(pattern)) {
         millis = int.tryParse(value);
       } else {
         return DateTime.tryParse(value);
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/fake_big_decimal_map200_response.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/fake_big_decimal_map200_response.dart
index bb878b52c06e..eae75fa0fa26 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/fake_big_decimal_map200_response.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/fake_big_decimal_map200_response.dart
@@ -71,9 +71,7 @@ class FakeBigDecimalMap200Response {
       }());
 
       return FakeBigDecimalMap200Response(
-        someId: json[r'someId'] == null
-            ? null
-            : num.parse(json[r'someId'].toString()),
+        someId: num.parse('${json[r'someId']}'),
         someMap: mapCastOfType<String, num>(json, r'someMap') ?? const {},
       );
     }
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/format_test.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/format_test.dart
index 9bacccfef3d7..67d169c4d8a2 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/format_test.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/format_test.dart
@@ -280,17 +280,15 @@ class FormatTest {
         integer: mapValueOfType<int>(json, r'integer'),
         int32: mapValueOfType<int>(json, r'int32'),
         int64: mapValueOfType<int>(json, r'int64'),
-        number: json[r'number'] == null
-            ? null
-            : num.parse(json[r'number'].toString()),
+        number: num.parse('${json[r'number']}'),
         float: mapValueOfType<double>(json, r'float'),
         double_: mapValueOfType<double>(json, r'double'),
         decimal: mapValueOfType<double>(json, r'decimal'),
         string: mapValueOfType<String>(json, r'string'),
         byte: mapValueOfType<String>(json, r'byte')!,
         binary: null, // No support for decoding binary content from JSON
-        date: mapDateTime(json, r'date', '')!,
-        dateTime: mapDateTime(json, r'dateTime', ''),
+        date: mapDateTime(json, r'date', r'')!,
+        dateTime: mapDateTime(json, r'dateTime', r''),
         uuid: mapValueOfType<String>(json, r'uuid'),
         password: mapValueOfType<String>(json, r'password')!,
         patternWithDigits: mapValueOfType<String>(json, r'pattern_with_digits'),
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/mixed_properties_and_additional_properties_class.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/mixed_properties_and_additional_properties_class.dart
index dfca68e14dce..976cbee2afea 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/mixed_properties_and_additional_properties_class.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/mixed_properties_and_additional_properties_class.dart
@@ -88,7 +88,7 @@ class MixedPropertiesAndAdditionalPropertiesClass {
 
       return MixedPropertiesAndAdditionalPropertiesClass(
         uuid: mapValueOfType<String>(json, r'uuid'),
-        dateTime: mapDateTime(json, r'dateTime', ''),
+        dateTime: mapDateTime(json, r'dateTime', r''),
         map: Animal.mapFromJson(json[r'map']),
       );
     }
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/nullable_class.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/nullable_class.dart
index 0a5a70afa506..ed9b75289ff2 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/nullable_class.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/nullable_class.dart
@@ -164,11 +164,11 @@ class NullableClass {
         integerProp: mapValueOfType<int>(json, r'integer_prop'),
         numberProp: json[r'number_prop'] == null
             ? null
-            : num.parse(json[r'number_prop'].toString()),
+            : num.parse('${json[r'number_prop']}'),
         booleanProp: mapValueOfType<bool>(json, r'boolean_prop'),
         stringProp: mapValueOfType<String>(json, r'string_prop'),
-        dateProp: mapDateTime(json, r'date_prop', ''),
-        datetimeProp: mapDateTime(json, r'datetime_prop', ''),
+        dateProp: mapDateTime(json, r'date_prop', r''),
+        datetimeProp: mapDateTime(json, r'datetime_prop', r''),
         arrayNullableProp: Object.listFromJson(json[r'array_nullable_prop']),
         arrayAndItemsNullableProp: Object.listFromJson(json[r'array_and_items_nullable_prop']),
         arrayItemsNullable: Object.listFromJson(json[r'array_items_nullable']),
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/number_only.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/number_only.dart
index 405f9f326b8b..74366c354254 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/number_only.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/number_only.dart
@@ -65,9 +65,7 @@ class NumberOnly {
       }());
 
       return NumberOnly(
-        justNumber: json[r'JustNumber'] == null
-            ? null
-            : num.parse(json[r'JustNumber'].toString()),
+        justNumber: num.parse('${json[r'JustNumber']}'),
       );
     }
     return null;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/object_with_deprecated_fields.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/object_with_deprecated_fields.dart
index 91932b3bc411..2afb378ba25b 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/object_with_deprecated_fields.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/object_with_deprecated_fields.dart
@@ -104,9 +104,7 @@ class ObjectWithDeprecatedFields {
 
       return ObjectWithDeprecatedFields(
         uuid: mapValueOfType<String>(json, r'uuid'),
-        id: json[r'id'] == null
-            ? null
-            : num.parse(json[r'id'].toString()),
+        id: num.parse('${json[r'id']}'),
         deprecatedRef: DeprecatedObject.fromJson(json[r'deprecatedRef']),
         bars: json[r'bars'] is Iterable
             ? (json[r'bars'] as Iterable).cast<String>().toList(growable: false)
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/order.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/order.dart
index 0894d4b295c5..e052dcc544a9 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/order.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/order.dart
@@ -133,7 +133,7 @@ class Order {
         id: mapValueOfType<int>(json, r'id'),
         petId: mapValueOfType<int>(json, r'petId'),
         quantity: mapValueOfType<int>(json, r'quantity'),
-        shipDate: mapDateTime(json, r'shipDate', ''),
+        shipDate: mapDateTime(json, r'shipDate', r''),
         status: OrderStatusEnum.fromJson(json[r'status']),
         complete: mapValueOfType<bool>(json, r'complete') ?? false,
       );
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/outer_composite.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/outer_composite.dart
index f0e549abf66a..2acc8f718dbb 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/outer_composite.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/outer_composite.dart
@@ -97,9 +97,7 @@ class OuterComposite {
       }());
 
       return OuterComposite(
-        myNumber: json[r'my_number'] == null
-            ? null
-            : num.parse(json[r'my_number'].toString()),
+        myNumber: num.parse('${json[r'my_number']}'),
         myString: mapValueOfType<String>(json, r'my_string'),
         myBoolean: mapValueOfType<bool>(json, r'my_boolean'),
       );