fix!: set duration to null when not present (#26982)

mobile/openapi/lib/model/asset_response_dto.dart

@@ -57,8 +57,8 @@ class AssetResponseDto {
   /// Duplicate group ID
   String? duplicateId;
 
-  /// Video duration (for videos)
-  String duration;
+  /// Video/gif duration in hh:mm:ss.SSS format (null for static images)
+  String? duration;
 
   ///
   /// Please note: This property should have been non-nullable! Since the specification file
@@ -209,7 +209,7 @@ class AssetResponseDto {
     (checksum.hashCode) +
     (createdAt.hashCode) +
     (duplicateId == null ? 0 : duplicateId!.hashCode) +
-    (duration.hashCode) +
+    (duration == null ? 0 : duration!.hashCode) +
     (exifInfo == null ? 0 : exifInfo!.hashCode) +
     (fileCreatedAt.hashCode) +
     (fileModifiedAt.hashCode) +
@@ -252,7 +252,11 @@ class AssetResponseDto {
     } else {
     //  json[r'duplicateId'] = null;
     }
+    if (this.duration != null) {
       json[r'duration'] = this.duration;
+    } else {
+    //  json[r'duration'] = null;
+    }
     if (this.exifInfo != null) {
       json[r'exifInfo'] = this.exifInfo;
     } else {
@@ -337,7 +341,7 @@ class AssetResponseDto {
         checksum: mapValueOfType<String>(json, r'checksum')!,
         createdAt: mapDateTime(json, r'createdAt', r'')!,
         duplicateId: mapValueOfType<String>(json, r'duplicateId'),
-        duration: mapValueOfType<String>(json, r'duration')!,
+        duration: mapValueOfType<String>(json, r'duration'),
         exifInfo: ExifResponseDto.fromJson(json[r'exifInfo']),
         fileCreatedAt: mapDateTime(json, r'fileCreatedAt', r'')!,
         fileModifiedAt: mapDateTime(json, r'fileModifiedAt', r'')!,

mobile/openapi/lib/model/time_bucket_asset_response_dto.dart

@@ -39,7 +39,7 @@ class TimeBucketAssetResponseDto {
   /// Array of country names extracted from EXIF GPS data
   List<String?> country;
 
-  /// Array of video durations in HH:MM:SS format (null for images)
+  /// Array of video/gif durations in hh:mm:ss.SSS format (null for static images)
   List<String?> duration;
 
   /// Array of file creation timestamps in UTC