NIFI-15653 Fix DeleteSFTP security check for dot directory path

nifi-extension-bundles/nifi-standard-bundle/nifi-standard-processors/src/main/java/org/apache/nifi/processors/standard/DeleteSFTP.java

@@ -211,7 +211,8 @@ public void onTrigger(ProcessContext context, ProcessSession session) throws Pro
                         filename = context.getProperty(FILENAME).evaluateAttributeExpressions(flowFile).getValue();
                         final Path filePath = directoryPath.resolve(filename).normalize();
 
-                        if (!directoryPath.equals(filePath.getParent())) {
+                        final Path fileParent = filePath.getParent();
+                        if (!directoryPath.equals(fileParent == null ? Paths.get("") : fileParent)) {
                             final String errorMessage = "Attempting to delete file at path '%s' which is not a direct child of the directory '%s'"
                                     .formatted(filePath, directoryPath);
 

nifi-extension-bundles/nifi-standard-bundle/nifi-standard-processors/src/test/java/org/apache/nifi/processors/standard/TestDeleteSFTP.java

@@ -154,6 +154,18 @@ void sendsFlowFileToSuccessWhenDeletingADirectoryAndDirectoryIsEmpty() throws IO
         runner.assertAllFlowFilesTransferred(DeleteSFTP.REL_SUCCESS);
     }
 
+    @Test
+    void deletesFileWhenDirectoryPathIsDot() throws IOException {
+        final Path fileToDelete = Files.writeString(sshServerRootPath.resolve("test.txt"), "some text");
+        enqueue(".", fileToDelete.getFileName().toString());
+        assertExists(fileToDelete);
+
+        runner.run();
+
+        assertNotExists(fileToDelete);
+        runner.assertAllFlowFilesTransferred(DeleteSFTP.REL_SUCCESS, 1);
+    }
+
     @Test
     void sendsFlowFileToFailureWhenFileIsNotADirectChildOfTheDirectory() throws IOException {
         final Path directoryPath = Files.createDirectories(sshServerRootPath.resolve("rel/path"));