Fix not correct mod installation

HMCLCore/src/main/java/org/jackhuang/hmcl/auth/yggdrasil/User.java

@@ -21,6 +21,7 @@ import com.google.gson.JsonParseException;
 
 import java.util.Map;
 
+import com.google.gson.annotations.JsonAdapter;
 import org.jackhuang.hmcl.util.Immutable;
 import org.jackhuang.hmcl.util.StringUtils;
 import org.jackhuang.hmcl.util.gson.Validation;
@@ -36,13 +37,14 @@ public final class User implements Validation {
     private final String id;
 
     @Nullable
+    @JsonAdapter(PropertyMapSerializer.class)
     private final Map<String, String> properties;
 
     public User(String id) {
         this(id, null);
     }
 
-    public User(String id, Map<String, String> properties) {
+    public User(String id, @Nullable Map<String, String> properties) {
         this.id = id;
         this.properties = properties;
     }
@@ -51,6 +53,7 @@ public final class User implements Validation {
         return id;
     }
 
+    @Nullable
     public Map<String, String> getProperties() {
         return properties;
     }

HMCLCore/src/main/java/org/jackhuang/hmcl/mod/ModManager.java

@@ -85,13 +85,15 @@ public final class ModManager {
 
     public void refreshMods() throws IOException {
         modInfos.clear();
-        for (Path subitem : Files.newDirectoryStream(getModsDirectory())) {
-            if (Files.isDirectory(subitem) && VersionNumber.isIntVersionNumber(FileUtils.getName(subitem))) {
-                // If the folder name is game version, forge will search mod in this subdirectory
-                for (Path subsubitem : Files.newDirectoryStream(subitem))
-                    addModInfo(subsubitem.toFile());
-            } else {
-                addModInfo(subitem.toFile());
+        if (Files.isDirectory(getModsDirectory())) {
+            for (Path subitem : Files.newDirectoryStream(getModsDirectory())) {
+                if (Files.isDirectory(subitem) && VersionNumber.isIntVersionNumber(FileUtils.getName(subitem))) {
+                    // If the folder name is game version, forge will search mod in this subdirectory
+                    for (Path subsubitem : Files.newDirectoryStream(subitem))
+                        addModInfo(subsubitem.toFile());
+                } else {
+                    addModInfo(subitem.toFile());
+                }
             }
         }
         loaded = true;