[dart] fix Date.toDateTime utc (#9717)

Author: FallenRiteMonk

modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/date.mustache

@@ -24,9 +24,10 @@ class Date implements Comparable<Date> {
   /// Convert to a [DateTime].
   DateTime toDateTime({bool utc = false}) {
     if (utc) {
-      DateTime.utc(year, month, day);
+      return DateTime.utc(year, month, day);
+    } else {
+      return DateTime(year, month, day);
     }
-    return DateTime(year, month, day);
   }
 
   @override
@@ -66,4 +67,4 @@ class Date implements Comparable<Date> {
 
 extension DateTimeToDate on DateTime {
   Date toDate() => Date(year, month, day);
-}
+}

samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/model/date.dart

@@ -24,9 +24,10 @@ class Date implements Comparable<Date> {
   /// Convert to a [DateTime].
   DateTime toDateTime({bool utc = false}) {
     if (utc) {
-      DateTime.utc(year, month, day);
+      return DateTime.utc(year, month, day);
+    } else {
+      return DateTime(year, month, day);
     }
-    return DateTime(year, month, day);
   }
 
   @override
@@ -66,4 +67,4 @@ class Date implements Comparable<Date> {
 
 extension DateTimeToDate on DateTime {
   Date toDate() => Date(year, month, day);
-}
+}