fixed nullpointer exception

ApiService/src/main/java/apiservice/repo/AssetRepo.java

@@ -3,6 +3,7 @@ package apiservice.repo;
 import apiservice.model.Asset;
 import org.springframework.stereotype.Repository;
 
+import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -19,6 +20,7 @@ public class AssetRepo implements IAssetRepo<Asset> {
 
     @Override
     public Asset save(Asset asset, String uid) {
+        repository.computeIfAbsent(uid, k -> new ArrayList<>());
         repository.get(uid).add(asset);
         return asset;
     }