Make versionless skins fallback to version 1.0

osu.Game.Tests/Skins/LegacySkinDecoderTest.cs

@@ -106,7 +106,7 @@ public void TestDecodeNoVersion()
             var decoder = new LegacySkinDecoder();
             using (var resStream = TestResources.OpenResource("skin-empty.ini"))
             using (var stream = new LineBufferedReader(resStream))
-                Assert.IsNull(decoder.Decode(stream).LegacyVersion);
+                Assert.That(decoder.Decode(stream).LegacyVersion, Is.EqualTo(1.0m));
         }
     }
 }

osu.Game/Skinning/LegacyBeatmapSkin.cs

@@ -2,6 +2,7 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using osu.Framework.Audio;
+using osu.Framework.Bindables;
 using osu.Framework.IO.Stores;
 using osu.Game.Beatmaps;
 
@@ -18,6 +19,20 @@ public LegacyBeatmapSkin(BeatmapInfo beatmap, IResourceStore<byte[]> storage, Au
             Configuration.AllowDefaultComboColoursFallback = false;
         }
 
+        public override IBindable<TValue> GetConfig<TLookup, TValue>(TLookup lookup)
+        {
+            switch (lookup)
+            {
+                case LegacySkinConfiguration.LegacySetting s when s == LegacySkinConfiguration.LegacySetting.Version:
+                    if (Configuration.LegacyVersion is decimal version)
+                        return SkinUtils.As<TValue>(new Bindable<decimal>(version));
+
+                    return null;
+            }
+
+            return base.GetConfig<TLookup, TValue>(lookup);
+        }
+
         private static SkinInfo createSkinInfo(BeatmapInfo beatmap) =>
             new SkinInfo { Name = beatmap.ToString(), Creator = beatmap.Metadata.Author.ToString() };
     }

osu.Game/Skinning/LegacySkin.cs

@@ -71,7 +71,7 @@ protected LegacySkin(SkinInfo skin, IResourceStore<byte[]> storage, AudioManager
                     }
                 }
                 else
-                    Configuration = new LegacySkinConfiguration { LegacyVersion = LegacySkinConfiguration.LATEST_VERSION };
+                    Configuration = new LegacySkinConfiguration();
             }
 
             if (storage != null)
@@ -122,10 +122,7 @@ public override IBindable<TValue> GetConfig<TLookup, TValue>(TLookup lookup)
                     switch (legacy)
                     {
                         case LegacySkinConfiguration.LegacySetting.Version:
-                            if (Configuration.LegacyVersion is decimal version)
+                            return SkinUtils.As<TValue>(new Bindable<decimal>(Configuration.LegacyVersion ?? LegacySkinConfiguration.LATEST_VERSION));
-                                return SkinUtils.As<TValue>(new Bindable<decimal>(version));
-
-                            break;
                     }
 
                     break;

osu.Game/Skinning/LegacySkinDecoder.cs

@@ -52,5 +52,12 @@ protected override void ParseLine(LegacySkinConfiguration skin, Section section,
 
             base.ParseLine(skin, section, line);
         }
+
+        protected override LegacySkinConfiguration CreateTemplateObject()
+        {
+            var config = base.CreateTemplateObject();
+            config.LegacyVersion = 1.0m;
+            return config;
+        }
     }
 }