diff --git a/src/DotTiled.Tests/Assert/AssertData.cs b/src/DotTiled.Tests/Assert/AssertData.cs
index d840ae0..6e8aaa2 100644
--- a/src/DotTiled.Tests/Assert/AssertData.cs
+++ b/src/DotTiled.Tests/Assert/AssertData.cs
@@ -18,13 +18,7 @@ public static partial class DotTiledAssert
     // Data
     AssertEqual(expected.GlobalTileIDs, actual.GlobalTileIDs, nameof(Data.GlobalTileIDs));
     AssertEqual(expected.FlippingFlags, actual.FlippingFlags, nameof(Data.FlippingFlags));
-
-    if (expected.Chunks.HasValue)
-    {
-      AssertEqual(expected.Chunks.Value.Length, actual.Chunks.Value.Length, "Chunks.Length");
-      for (var i = 0; i < expected.Chunks.Value.Length; i++)
-        AssertChunk(expected.Chunks.Value[i], actual.Chunks.Value[i]);
-    }
+    AssertOptionalsEqual(expected.Chunks, actual.Chunks, nameof(Data.Chunks), (a, b) => AssertListOrdered(a, b, nameof(Chunk), AssertChunk));
   }
 
   private static void AssertChunk(Chunk expected, Chunk actual)
diff --git a/src/DotTiled/Layers/Data.cs b/src/DotTiled/Layers/Data.cs
index d5dea5b..16bf34e 100644
--- a/src/DotTiled/Layers/Data.cs
+++ b/src/DotTiled/Layers/Data.cs
@@ -130,12 +130,12 @@ public class Data
   /// To get an actual tile ID, you map it to a local tile ID using the correct tileset. Please refer to
   /// <see href="https://doc.mapeditor.org/en/stable/reference/global-tile-ids/#mapping-a-gid-to-a-local-tile-id">the documentation on how to do this</see>.
   /// </summary>
-  public uint[] GlobalTileIDs { get; set; }
+  public Optional<uint[]> GlobalTileIDs { get; set; } = Optional<uint[]>.Empty;
 
   /// <summary>
   /// The parsed flipping flags for each tile in the layer. Appear in the same order as the tiles in the layer in <see cref="GlobalTileIDs"/>.
   /// </summary>
-  public FlippingFlags[] FlippingFlags { get; set; }
+  public Optional<FlippingFlags[]> FlippingFlags { get; set; } = Optional<FlippingFlags[]>.Empty;
 
   /// <summary>
   /// If the map is infinite, it will instead contain a list of chunks.
diff --git a/src/DotTiled/Serialization/Tmj/TmjReaderBase.Data.cs b/src/DotTiled/Serialization/Tmj/TmjReaderBase.Data.cs
index f42ddd5..47b9b75 100644
--- a/src/DotTiled/Serialization/Tmj/TmjReaderBase.Data.cs
+++ b/src/DotTiled/Serialization/Tmj/TmjReaderBase.Data.cs
@@ -13,9 +13,7 @@ public abstract partial class TmjReaderBase
     {
       Chunks = chunks,
       Compression = compression,
-      Encoding = encoding,
-      FlippingFlags = null,
-      GlobalTileIDs = null
+      Encoding = encoding
     };
   }
 
@@ -34,8 +32,8 @@ public abstract partial class TmjReaderBase
       Y = y,
       Width = width,
       Height = height,
-      GlobalTileIDs = data.GlobalTileIDs!,
-      FlippingFlags = data.FlippingFlags!
+      GlobalTileIDs = data.GlobalTileIDs,
+      FlippingFlags = data.FlippingFlags
     };
   }
 
@@ -46,7 +44,7 @@ public abstract partial class TmjReaderBase
       // Array of uint
       var data = element.GetValueAsList<uint>(e => e.GetValueAs<uint>()).ToArray();
       var (globalTileIDs, flippingFlags) = Helpers.ReadAndClearFlippingFlagsFromGIDs(data);
-      return new Data { Encoding = encoding, Compression = compression, GlobalTileIDs = globalTileIDs, FlippingFlags = flippingFlags, Chunks = null };
+      return new Data { Encoding = encoding, Compression = compression, GlobalTileIDs = globalTileIDs, FlippingFlags = flippingFlags };
     }
     else if (encoding == DataEncoding.Base64)
     {
@@ -56,7 +54,7 @@ public abstract partial class TmjReaderBase
       {
         var data = Helpers.ReadBytesAsInt32Array(base64Data);
         var (globalTileIDs, flippingFlags) = Helpers.ReadAndClearFlippingFlagsFromGIDs(data);
-        return new Data { Encoding = encoding, Compression = compression, GlobalTileIDs = globalTileIDs, FlippingFlags = flippingFlags, Chunks = null };
+        return new Data { Encoding = encoding, Compression = compression, GlobalTileIDs = globalTileIDs, FlippingFlags = flippingFlags };
       }
 
       using var stream = new MemoryStream(base64Data);
@@ -70,7 +68,7 @@ public abstract partial class TmjReaderBase
 
       {
         var (globalTileIDs, flippingFlags) = Helpers.ReadAndClearFlippingFlagsFromGIDs(decompressed);
-        return new Data { Encoding = encoding, Compression = compression, GlobalTileIDs = globalTileIDs, FlippingFlags = flippingFlags, Chunks = null };
+        return new Data { Encoding = encoding, Compression = compression, GlobalTileIDs = globalTileIDs, FlippingFlags = flippingFlags };
       }
     }
 
diff --git a/src/DotTiled/Serialization/Tmx/TmxReaderBase.Data.cs b/src/DotTiled/Serialization/Tmx/TmxReaderBase.Data.cs
index 4c196fa..a05bbd0 100644
--- a/src/DotTiled/Serialization/Tmx/TmxReaderBase.Data.cs
+++ b/src/DotTiled/Serialization/Tmx/TmxReaderBase.Data.cs
@@ -30,7 +30,7 @@ public abstract partial class TmxReaderBase
       var chunks = _reader
         .ReadList("data", "chunk", (r) => ReadChunk(encoding, compression))
         .ToArray();
-      return new Data { Encoding = encoding, Compression = compression, GlobalTileIDs = null, Chunks = chunks };
+      return new Data { Encoding = encoding, Compression = compression, Chunks = chunks };
     }
 
     var usesTileChildrenInsteadOfRawData = !encoding.HasValue && !compression.HasValue;
@@ -38,12 +38,12 @@ public abstract partial class TmxReaderBase
     {
       var tileChildrenGlobalTileIDsWithFlippingFlags = ReadTileChildrenInWrapper("data", _reader);
       var (tileChildrenGlobalTileIDs, tileChildrenFlippingFlags) = ReadAndClearFlippingFlagsFromGIDs(tileChildrenGlobalTileIDsWithFlippingFlags);
-      return new Data { Encoding = encoding, Compression = compression, GlobalTileIDs = tileChildrenGlobalTileIDs, FlippingFlags = tileChildrenFlippingFlags, Chunks = null };
+      return new Data { Encoding = encoding, Compression = compression, GlobalTileIDs = tileChildrenGlobalTileIDs, FlippingFlags = tileChildrenFlippingFlags };
     }
 
     var rawDataGlobalTileIDsWithFlippingFlags = ReadRawData(_reader, encoding, compression);
     var (rawDataGlobalTileIDs, rawDataFlippingFlags) = ReadAndClearFlippingFlagsFromGIDs(rawDataGlobalTileIDsWithFlippingFlags);
-    return new Data { Encoding = encoding, Compression = compression, GlobalTileIDs = rawDataGlobalTileIDs, FlippingFlags = rawDataFlippingFlags, Chunks = null };
+    return new Data { Encoding = encoding, Compression = compression, GlobalTileIDs = rawDataGlobalTileIDs, FlippingFlags = rawDataFlippingFlags };
   }
 
   internal static (uint[] GlobalTileIDs, FlippingFlags[] FlippingFlags) ReadAndClearFlippingFlagsFromGIDs(uint[] globalTileIDs)