diff --git a/HMCLCore/src/main/java/org/jackhuang/hmcl/download/game/LibraryDownloadException.java b/HMCLCore/src/main/java/org/jackhuang/hmcl/download/game/LibraryDownloadException.java
index 086402830..10af82acb 100644
--- a/HMCLCore/src/main/java/org/jackhuang/hmcl/download/game/LibraryDownloadException.java
+++ b/HMCLCore/src/main/java/org/jackhuang/hmcl/download/game/LibraryDownloadException.java
@@ -18,11 +18,12 @@
 package org.jackhuang.hmcl.download.game;
 
 import org.jackhuang.hmcl.game.Library;
+import org.jetbrains.annotations.NotNull;
 
 public class LibraryDownloadException extends Exception {
     private final Library library;
 
-    public LibraryDownloadException(Library library, Throwable cause) {
+    public LibraryDownloadException(Library library, @NotNull Throwable cause) {
         super("Unable to download library " + library, cause);
 
         this.library = library;
diff --git a/HMCLCore/src/main/java/org/jackhuang/hmcl/download/game/LibraryDownloadTask.java b/HMCLCore/src/main/java/org/jackhuang/hmcl/download/game/LibraryDownloadTask.java
index 106fbc367..3d308940c 100644
--- a/HMCLCore/src/main/java/org/jackhuang/hmcl/download/game/LibraryDownloadTask.java
+++ b/HMCLCore/src/main/java/org/jackhuang/hmcl/download/game/LibraryDownloadTask.java
@@ -37,6 +37,7 @@ import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.*;
+import java.util.concurrent.CancellationException;
 import java.util.jar.*;
 import java.util.logging.Level;
 
@@ -95,6 +96,8 @@ public class LibraryDownloadTask extends Task<Void> {
             Exception t = task.getException();
             if (t instanceof DownloadException)
                 throw new LibraryDownloadException(library, t.getCause());
+            else if (t == null)
+                throw new CancellationException();
             else
                 throw new LibraryDownloadException(library, t);
         } else {
diff --git a/HMCLCore/src/main/java/org/jackhuang/hmcl/task/DownloadException.java b/HMCLCore/src/main/java/org/jackhuang/hmcl/task/DownloadException.java
index e6411410b..55d7b1cc7 100644
--- a/HMCLCore/src/main/java/org/jackhuang/hmcl/task/DownloadException.java
+++ b/HMCLCore/src/main/java/org/jackhuang/hmcl/task/DownloadException.java
@@ -17,6 +17,8 @@
  */
 package org.jackhuang.hmcl.task;
 
+import org.jetbrains.annotations.NotNull;
+
 import java.io.IOException;
 import java.net.URL;
 
@@ -26,7 +28,7 @@ public class DownloadException extends IOException {
 
     private final URL url;
 
-    public DownloadException(URL url, Throwable cause) {
+    public DownloadException(URL url, @NotNull Throwable cause) {
         super("Unable to download " + url + ", " + cause.getMessage(), requireNonNull(cause));
 
         this.url = url;
diff --git a/HMCLCore/src/main/java/org/jackhuang/hmcl/task/Task.java b/HMCLCore/src/main/java/org/jackhuang/hmcl/task/Task.java
index 44782c7b8..f2441025a 100644
--- a/HMCLCore/src/main/java/org/jackhuang/hmcl/task/Task.java
+++ b/HMCLCore/src/main/java/org/jackhuang/hmcl/task/Task.java
@@ -31,6 +31,7 @@ import org.jackhuang.hmcl.util.function.ExceptionalConsumer;
 import org.jackhuang.hmcl.util.function.ExceptionalFunction;
 import org.jackhuang.hmcl.util.function.ExceptionalRunnable;
 import org.jackhuang.hmcl.util.function.ExceptionalSupplier;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.*;
 import java.util.concurrent.Callable;
@@ -131,6 +132,7 @@ public abstract class Task<T> {
      *
      * @return the exception thrown during execution, possibly from dependents or dependencies.
      */
+    @Nullable
     public final Exception getException() {
         return exception;
     }