diff --git a/HMCL/src/main/java/org/jackhuang/hellominecraft/launcher/core/asset/AssetsMojangLoader.java b/HMCL/src/main/java/org/jackhuang/hellominecraft/launcher/core/asset/AssetsMojangLoader.java
index d1efa9ef5..7342d64fb 100755
--- a/HMCL/src/main/java/org/jackhuang/hellominecraft/launcher/core/asset/AssetsMojangLoader.java
+++ b/HMCL/src/main/java/org/jackhuang/hellominecraft/launcher/core/asset/AssetsMojangLoader.java
@@ -32,6 +32,7 @@ import org.jackhuang.hellominecraft.util.system.IOUtils;
 import org.jackhuang.hellominecraft.util.StrUtils;
 import org.jackhuang.hellominecraft.launcher.core.download.IDownloadProvider;
 import org.jackhuang.hellominecraft.launcher.core.version.MinecraftVersion;
+import org.jackhuang.hellominecraft.util.Utils;
 import org.jackhuang.hellominecraft.util.VersionNumber;
 import org.jackhuang.hellominecraft.util.tasks.TaskInfo;
 
@@ -47,8 +48,7 @@ public class AssetsMojangLoader extends IAssetsHandler {
 
     @Override
     public Task getList(final MinecraftVersion mv, final IMinecraftAssetService mp) {
-        if (mv == null)
-            throw new IllegalArgumentException("AssetsMojangLoader: null argument: MinecraftVersion");
+        Utils.requireNonNull(mv);
         String assetsId = mv.getAssetsIndex().getId();
         File assets = mp.getAssets();
         HMCLog.log("Gathering asset index: " + assetsId);
diff --git a/HMCL/src/main/java/org/jackhuang/hellominecraft/launcher/core/asset/MinecraftAssetService.java b/HMCL/src/main/java/org/jackhuang/hellominecraft/launcher/core/asset/MinecraftAssetService.java
index ca7578714..6d0c29b65 100755
--- a/HMCL/src/main/java/org/jackhuang/hellominecraft/launcher/core/asset/MinecraftAssetService.java
+++ b/HMCL/src/main/java/org/jackhuang/hellominecraft/launcher/core/asset/MinecraftAssetService.java
@@ -30,6 +30,7 @@ import org.jackhuang.hellominecraft.launcher.core.service.IMinecraftService;
 import org.jackhuang.hellominecraft.launcher.core.version.AssetIndexDownloadInfo;
 import org.jackhuang.hellominecraft.launcher.core.version.MinecraftVersion;
 import org.jackhuang.hellominecraft.util.MessageBox;
+import org.jackhuang.hellominecraft.util.Utils;
 import org.jackhuang.hellominecraft.util.func.Function;
 import org.jackhuang.hellominecraft.util.logging.HMCLog;
 import org.jackhuang.hellominecraft.util.tasks.Task;
@@ -55,6 +56,7 @@ public class MinecraftAssetService extends IMinecraftAssetService {
     }
 
     public Task downloadAssets(final MinecraftVersion mv) {
+        Utils.requireNonNull(mv);
         return new TaskInfo("Download Assets") {
             Collection<Task> afters = new HashSet<>();
 
diff --git a/HMCL/src/main/java/org/jackhuang/hellominecraft/launcher/core/download/MinecraftDownloadService.java b/HMCL/src/main/java/org/jackhuang/hellominecraft/launcher/core/download/MinecraftDownloadService.java
index fac9b24e4..802af8a09 100755
--- a/HMCL/src/main/java/org/jackhuang/hellominecraft/launcher/core/download/MinecraftDownloadService.java
+++ b/HMCL/src/main/java/org/jackhuang/hellominecraft/launcher/core/download/MinecraftDownloadService.java
@@ -54,16 +54,15 @@ public class MinecraftDownloadService extends IMinecraftDownloadService {
         if (mv == null)
             return downloadLibraries;
         MinecraftVersion v = mv.resolve(service.version());
-        if (v.libraries != null)
-            for (IMinecraftLibrary l : v.libraries)
-                if (l.allow()) {
-                    File ff = l.getFilePath(service.baseDirectory());
-                    if (!ff.exists()) {
-                        String libURL = l.getDownloadInfo().getUrl(service.getDownloadType());
-                        if (libURL != null)
-                            downloadLibraries.add(new DownloadLibraryJob(l, libURL, ff));
-                    }
+        for (IMinecraftLibrary l : v.getLibraries())
+            if (l != null && l.allow()) {
+                File ff = l.getFilePath(service.baseDirectory());
+                if (!ff.exists()) {
+                    String libURL = l.getDownloadInfo().getUrl(service.getDownloadType());
+                    if (libURL != null)
+                        downloadLibraries.add(new DownloadLibraryJob(l, libURL, ff));
                 }
+            }
         return downloadLibraries;
     }
 
diff --git a/HMCL/src/main/java/org/jackhuang/hellominecraft/launcher/core/version/MinecraftVersion.java b/HMCL/src/main/java/org/jackhuang/hellominecraft/launcher/core/version/MinecraftVersion.java
index cd193df12..eb3d32512 100755
--- a/HMCL/src/main/java/org/jackhuang/hellominecraft/launcher/core/version/MinecraftVersion.java
+++ b/HMCL/src/main/java/org/jackhuang/hellominecraft/launcher/core/version/MinecraftVersion.java
@@ -168,4 +168,8 @@ public class MinecraftVersion implements Cloneable, Comparable<MinecraftVersion>
             i.id = id;
         return i;
     }
+
+    public Set<IMinecraftLibrary> getLibraries() {
+        return libraries == null ? new HashSet() : new HashSet(libraries);
+    }
 }