diff --git a/src/N_m3u8DL-RE/DownloadManager/SimpleDownloadManager.cs b/src/N_m3u8DL-RE/DownloadManager/SimpleDownloadManager.cs
index 523e560..f65cf52 100644
--- a/src/N_m3u8DL-RE/DownloadManager/SimpleDownloadManager.cs
+++ b/src/N_m3u8DL-RE/DownloadManager/SimpleDownloadManager.cs
@@ -68,7 +68,7 @@ namespace N_m3u8DL_RE.DownloadManager
                 Logger.WarnMarkUp($"[darkorange3_1]{ResString.autoBinaryMerge2}[/]");
             }
 
-            if (mediainfos.Where(m => m.Type == "Audio").All(m => m.BaseInfo.Contains("aac")))
+            if (mediainfos.Where(m => m.Type == "Audio").All(m => m.BaseInfo!.Contains("aac")))
             {
                 useAACFilter = true;
             }
diff --git a/src/N_m3u8DL-RE/Entity/Mediainfo.cs b/src/N_m3u8DL-RE/Entity/Mediainfo.cs
index c3daa6b..ae019b5 100644
--- a/src/N_m3u8DL-RE/Entity/Mediainfo.cs
+++ b/src/N_m3u8DL-RE/Entity/Mediainfo.cs
@@ -9,19 +9,19 @@ namespace N_m3u8DL_RE.Entity
 {
     internal class Mediainfo
     {
-        public string Id { get; set; }
-        public string Text { get; set; }
-        public string BaseInfo { get; set; }
-        public string Bitrate { get; set; }
-        public string Resolution { get; set; }
-        public string Fps { get; set; }
-        public string Type { get; set; }
+        public string? Id { get; set; }
+        public string? Text { get; set; }
+        public string? BaseInfo { get; set; }
+        public string? Bitrate { get; set; }
+        public string? Resolution { get; set; }
+        public string? Fps { get; set; }
+        public string? Type { get; set; }
         public bool DolbyVison { get; set; }
         public bool HDR { get; set; }
 
         public override string? ToString()
         {
-            return $"{(string.IsNullOrEmpty(Id) ? "NaN" : Id)}: " + string.Join(", ", new List<string> { Type, BaseInfo, Resolution, Fps, Bitrate }.Where(i => !string.IsNullOrEmpty(i)));
+            return $"{(string.IsNullOrEmpty(Id) ? "NaN" : Id)}: " + string.Join(", ", new List<string?> { Type, BaseInfo, Resolution, Fps, Bitrate }.Where(i => !string.IsNullOrEmpty(i)));
         }
 
         public string ToStringMarkUp()