[NO ISSUE][OTH] Check folder exists when loading a directory

- user model changes: no
- storage format changes: no
- interface changes: no

Details:
When loading a directory to S3Mock, check if the directory
already exists.

Change-Id: I8709370239d39512c87d94b3232e773275887ccf
Reviewed-on: https://asterix-gerrit.ics.uci.edu/c/asterixdb/+/17710
Integration-Tests: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Reviewed-by: Hussain Towaileb <hussainht@gmail.com>
Tested-by: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
diff --git a/asterixdb/asterix-app/src/test/java/org/apache/asterix/test/external_dataset/ExternalDatasetTestUtils.java b/asterixdb/asterix-app/src/test/java/org/apache/asterix/test/external_dataset/ExternalDatasetTestUtils.java
index b50c353..7da2334 100644
--- a/asterixdb/asterix-app/src/test/java/org/apache/asterix/test/external_dataset/ExternalDatasetTestUtils.java
+++ b/asterixdb/asterix-app/src/test/java/org/apache/asterix/test/external_dataset/ExternalDatasetTestUtils.java
@@ -283,7 +283,12 @@
     }
 
     private static void loadDirectory(String dataBasePath, String rootPath, FilenameFilter filter) {
-        Collection<File> files = IoUtil.getMatchingFiles(Path.of(dataBasePath, rootPath), filter);
+        File dir = new File(dataBasePath, rootPath);
+        if (!dir.exists() || !dir.isDirectory()) {
+            return;
+        }
+
+        Collection<File> files = IoUtil.getMatchingFiles(dir.toPath(), filter);
         int size = 0;
         for (File file : files) {
             String path = file.getPath();