diff --git a/judgels-backends/judgels-commons/judgels-fs/src/main/java/judgels/fs/local/LocalFileSystem.java b/judgels-backends/judgels-commons/judgels-fs/src/main/java/judgels/fs/local/LocalFileSystem.java
index 3ce7a7cd9..0efbaca28 100644
--- a/judgels-backends/judgels-commons/judgels-fs/src/main/java/judgels/fs/local/LocalFileSystem.java
+++ b/judgels-backends/judgels-commons/judgels-fs/src/main/java/judgels/fs/local/LocalFileSystem.java
@@ -47,7 +47,9 @@ public LocalFileSystem(Path baseDir) {
     @Override
     public void createDirectory(Path dirPath) {
         try {
-            Files.createDirectories(baseDir.resolve(dirPath), PosixFilePermissions.asFileAttribute(PERMISSION_700));
+            Files.createDirectories(
+                    dirPath == null ? baseDir : baseDir.resolve(dirPath),
+                    PosixFilePermissions.asFileAttribute(PERMISSION_700));
         } catch (IOException e) {
             throw new RuntimeException(e);
         }