Close the command scanner once stopped

src/main/java/net/minestom/server/command/CommandManager.java

@@ -61,6 +61,7 @@ public final class CommandManager {
                     execute(consoleSender, command);
                 }
             }
+            scanner.close();
         }, "ConsoleCommand-Thread");
         consoleThread.setDaemon(true);
         consoleThread.start();

src/main/java/net/minestom/server/data/DataImpl.java

@@ -21,7 +21,7 @@ public class DataImpl implements Data {
     protected final ConcurrentHashMap<String, Class> dataType = new ConcurrentHashMap<>();
 
     @Override
-    public <T> void set(@NotNull String key, @Nullable T value, @Nullable Class<T> type) {
+    public synchronized <T> void set(@NotNull String key, @Nullable T value, @Nullable Class<T> type) {
         if (value != null) {
             this.data.put(key, value);
             this.dataType.put(key, type);

src/main/java/net/minestom/server/entity/PlayerSkin.java

@@ -86,9 +86,11 @@ public class PlayerSkin {
         final String url = "https://api.mojang.com/users/profiles/minecraft/" + username;
 
         try {
+            // Retrieve the mojang uuid from the name
             final String response = URLUtils.getText(url);
             final JsonObject jsonObject = JsonParser.parseString(response).getAsJsonObject();
             final String uuid = jsonObject.get("id").getAsString();
+            // Retrieve the skin data from the mojang uuid
             return fromUuid(uuid);
         } catch (IOException e) {
             e.printStackTrace();