FileSystemProvider::checkAccess fails on '/' with StorageException (g…

…oogleapis#1065)

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:
- [x] Make sure to open an issue: https://togithub.com/googleapis/java-storage-nio/issues/1062
- [x] Ensure the tests and linter pass
- [x] Code coverage does not decrease (if any source code was changed)
- [x] Appropriate docs were updated (if necessary)

Fixes googleapis#1062 ☕️

google-cloud-nio/src/main/java/com/google/cloud/storage/contrib/nio/CloudStorageFileSystemProvider.java

@@ -728,6 +728,11 @@ public void checkAccess(Path path, AccessMode... modes) throws IOException {
     // Loop will terminate via an exception if all retries are exhausted
     while (true) {
       try {
+        // Edge case is the root directory which triggers the storage.get to throw a
+        // StorageException.
+        if (cloudPath.normalize().equals(cloudPath.getRoot())) {
+          return;
+        }
         boolean nullId;
         if (isNullOrEmpty(userProject)) {
           nullId =

google-cloud-nio/src/test/java/com/google/cloud/storage/contrib/nio/it/ITGcsNio.java

@@ -53,6 +53,7 @@
 import java.nio.channels.FileChannel;
 import java.nio.channels.ReadableByteChannel;
 import java.nio.channels.SeekableByteChannel;
+import java.nio.file.AccessMode;
 import java.nio.file.FileAlreadyExistsException;
 import java.nio.file.FileSystem;
 import java.nio.file.FileVisitResult;
@@ -63,6 +64,7 @@
 import java.nio.file.StandardCopyOption;
 import java.nio.file.StandardOpenOption;
 import java.nio.file.attribute.BasicFileAttributes;
+import java.nio.file.spi.FileSystemProvider;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
@@ -1196,6 +1198,16 @@ public void testCopy_replaceFile_withOption_srcDoesNotExist() throws IOException
     }
   }
 
+  @Test
+  public void testCheckAccessRoot() throws Exception {
+    FileSystem fileSystem = getTestBucket();
+    Path path = fileSystem.getPath("/");
+    FileSystemProvider provider = fileSystem.provider();
+
+    // Against the real cloud storage this used to throw a StorageException.
+    provider.checkAccess(path, AccessMode.READ, AccessMode.WRITE);
+  }
+
   private CloudStorageFileSystem getTestBucket() throws IOException {
     // in typical usage we use the single-argument version of forBucket
     // and rely on the user being logged into their project with the