add fallback head (steve)

src/main/java/cc/fascinated/api/controller/PlayerController.java

@@ -4,6 +4,7 @@ import cc.fascinated.player.PlayerManagerService;
 import cc.fascinated.player.impl.Player;
 import cc.fascinated.player.impl.Skin;
 import cc.fascinated.player.impl.SkinPart;
+import lombok.NonNull;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.http.CacheControl;
 import org.springframework.http.HttpStatus;
@@ -12,12 +13,14 @@ import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.*;
 
 import java.util.Map;
+import java.util.Objects;
 import java.util.concurrent.TimeUnit;
 
 @RestController
 @RequestMapping(value = "/")
 public class PlayerController {
 
+    @NonNull private final SkinPart defaultHead = Objects.requireNonNull(Skin.getDefaultHead(), "Default head is null");
     private final PlayerManagerService playerManagerService;
 
     @Autowired
@@ -37,15 +40,17 @@ public class PlayerController {
     @GetMapping(value = "/avatar/{id}")
     public ResponseEntity<byte[]> getPlayerHead(@PathVariable String id) {
         Player player = playerManagerService.getPlayer(id);
+        byte[] headBytes;
         if (player == null) {
-            return null;
+            headBytes = defaultHead.getPartData();
+        } else {
+            Skin skin = player.getSkin();
+            SkinPart head = skin.getHead();
+            headBytes = head.getPartData();
         }
-
-        Skin skin = player.getSkin();
-        SkinPart head = skin.getHead();
         return ResponseEntity.ok()
                 .cacheControl(CacheControl.maxAge(1, TimeUnit.HOURS).cachePublic())
                 .contentType(MediaType.IMAGE_PNG)
-                .body(head.getPartData());
+                .body(headBytes);
     }
 }