some improvements

-  do not throw exception if file is empty
- DataPlist should initialized before save
- fallback for empty input in level decompress
- rollback base64 lib to 0.1.2

GeometryDashAPI/Data/GameData.cs

@@ -14,7 +14,7 @@ public class GameData
         // see more https://en.wikipedia.org/wiki/Gzip
         private static readonly byte[] XorDatFileMagickBytes = [ 0x43, 0x3f ];
 
-        public Plist DataPlist { get; set; }
+        public Plist? DataPlist { get; set; }
 
         private readonly GameDataType? type;
 
@@ -51,13 +51,12 @@ public virtual async Task LoadAsync(string fileName)
             // windows files
             var xor = Crypt.XOR(data, 0xB);
             var index = xor.AsSpan().IndexOf((byte)0);
-            var gZipDecompress =
-                Crypt.GZipDecompress(
-                    GameConvert.FromBase64(Encoding.ASCII.GetString(xor, 0, index >= 0 ? index : xor.Length)));
-
-            if (gZipDecompress is null)
-                throw new InvalidOperationException("Data was empty");
-
+            var gZipDecompress = Crypt.GZipDecompress(GameConvert.FromBase64(Encoding.ASCII.GetString(xor, 0, index >= 0 ? index : xor.Length)));
+            if (gZipDecompress == null)
+            {
+                DataPlist = [];
+                return;
+            }
             DataPlist = new Plist(gZipDecompress);
         }
 
@@ -75,6 +74,8 @@ public virtual async Task LoadAsync(string fileName)
         public void Save(string? fullName = null, DatFileFormat? format = null)
         {
             using var memory = new MemoryStream();
+            if (DataPlist == null)
+                throw new InvalidOperationException($"nothing to save: {nameof(DataPlist)} is null");
             DataPlist.SaveToStream(memory);
             File.WriteAllBytes(fullName ?? ResolveFileName(type), GetFileContent(memory, format ?? ResolveFileFormat()));
         }
@@ -93,6 +94,8 @@ public void Save(string? fullName = null, DatFileFormat? format = null)
         public async Task SaveAsync(string? fileName = null, DatFileFormat? format = null)
         {
             using var memory = new MemoryStream();
+            if (DataPlist == null)
+                throw new InvalidOperationException($"nothing to save: {nameof(DataPlist)} is null");
             await DataPlist.SaveToStreamAsync(memory);
 #if NETSTANDARD2_1
             await File.WriteAllBytesAsync(fileName ?? ResolveFileName(type), GetFileContent(memory, format ?? ResolveFileFormat()));

GeometryDashAPI/GeometryDashAPI.csproj

@@ -28,7 +28,7 @@
     <PackageReference Include="csFastFloat" Version="4.1.4" />
     <PackageReference Include="Microsoft.CSharp" Version="4.7.0" />
     <PackageReference Include="SharpZipLib" Version="1.4.2" />
-    <PackageReference Include="UrlBase64" Version="1.0.1" />
+    <PackageReference Include="UrlBase64" Version="0.1.2" />
   </ItemGroup>
 
   <ItemGroup>

GeometryDashAPI/Levels/Level.cs

@@ -111,10 +111,10 @@ public static string Decompress(string data)
             var bytes = GameConvert.FromBase64(data);
 
             if (bytes[0] == 0x78)
-                return Crypt.ZLibDecompress(bytes)?.StreamToString();
+                return Crypt.ZLibDecompress(bytes)?.StreamToString() ?? string.Empty;
 
             if (bytes[0] == 0x1F && bytes[1] == 0x8B)
-                return Crypt.GZipDecompress(bytes)?.StreamToString();
+                return Crypt.GZipDecompress(bytes)?.StreamToString() ?? string.Empty;
 
             throw new InvalidOperationException(
                 "Unsupported data signature. There is no gzip and zlib. Please check your level data. If your level is correct and works in the game, please create an issue: https://github.com/Folleach/GeometryDashAPI/issues. Or fix it yourself: https://github.com/Folleach/GeometryDashAPI/blob/master/GeometryDashAPI/Levels/Level.cs");