fix error message

ml-algorithms/src/main/java/org/opensearch/ml/engine/ModelHelper.java

@@ -229,7 +229,12 @@ public void downloadAndSplit(
                 DownloadUtils.download(url, modelPath, new ProgressBar());
                 verifyModelZipFile(modelFormat, modelPath, modelName, functionName);
                 String hash = calculateFileHash(modelZipFile);
-                if (hash.equals(modelContentHash)) {
+                if (modelContentHash == null) {
+                    log.error("Hash code need to be provided when register via url.");
+                    throw (new IllegalArgumentException(
+                        "Model content Hash code need to be provided when register via url. Please calculate sha 256 Hash code."
+                    ));
+                } else if (hash.equals(modelContentHash)) {
                     List<String> chunkFiles = splitFileIntoChunks(modelZipFile, modelPartsPath, CHUNK_SIZE);
                     Map<String, Object> result = new HashMap<>();
                     result.put(CHUNK_FILES, chunkFiles);

ml-algorithms/src/test/java/org/opensearch/ml/engine/algorithms/text_embedding/ModelHelperTest.java

@@ -85,6 +85,15 @@ public void testDownloadAndSplit() throws URISyntaxException {
         assertNotEquals(0, argumentCaptor.getValue().size());
     }
 
+    @Test
+    public void testDownloadAndSplit_nullHashCode() throws URISyntaxException {
+        String modelUrl = getClass().getResource("traced_small_model.zip").toURI().toString();
+        modelHelper.downloadAndSplit(modelFormat, modelId, "model_name", "1", modelUrl, null, FunctionName.TEXT_EMBEDDING, actionListener);
+        ArgumentCaptor<Exception> argumentCaptor = ArgumentCaptor.forClass(Exception.class);
+        verify(actionListener).onFailure(argumentCaptor.capture());
+        assertEquals(IllegalArgumentException.class, argumentCaptor.getValue().getClass());
+    }
+
     @Test
     public void testDownloadAndSplit_HashFailure() throws URISyntaxException {
         String modelUrl = getClass().getResource("traced_small_model.zip").toURI().toString();

plugin/src/main/java/org/opensearch/ml/action/deploy/TransportDeployModelAction.java

@@ -226,6 +226,8 @@ private void deployModel(
                                 "Model already deployed to these nodes: "
                                     + Arrays.toString(difference.toArray(new String[0]))
                                     + ", but they are not included in target node ids. Undeploy model from these nodes if don't need them any more."
+                                    + "Undeploy from old nodes before try to deploy model on new nodes. Or include all old nodes on your target nodes."
+
                             )
                         );
                     return;