diff --git a/common/src/main/java/org/opensearch/ml/common/connector/HttpConnector.java b/common/src/main/java/org/opensearch/ml/common/connector/HttpConnector.java
index 82d19bdb01..96f6c018ec 100644
--- a/common/src/main/java/org/opensearch/ml/common/connector/HttpConnector.java
+++ b/common/src/main/java/org/opensearch/ml/common/connector/HttpConnector.java
@@ -26,6 +26,8 @@
 import java.util.Map;
 import java.util.Optional;
 import java.util.function.Function;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 import static org.opensearch.core.xcontent.XContentParserUtils.ensureExpectedToken;
 import static org.opensearch.ml.common.connector.ConnectorProtocols.HTTP;
@@ -82,7 +84,7 @@ public HttpConnector(String protocol, XContentParser parser) throws IOException
                     description = parser.text();
                     break;
                 case PROTOCOL_FIELD:
-                    protocol = parser.text();
+                    this.protocol = parser.text();
                     break;
                 case PARAMETERS_FIELD:
                     Map<String, Object> map = parser.map();
@@ -251,6 +253,7 @@ public  <T> T createPredictPayload(Map<String, String> parameters) {
         Optional<ConnectorAction> predictAction = findPredictAction();
         if (predictAction.isPresent() && predictAction.get().getRequestBody() != null) {
             String payload = predictAction.get().getRequestBody();
+            payload = fillNullParameters(parameters, payload);
             StringSubstitutor substitutor = new StringSubstitutor(parameters, "${parameters.", "}");
             payload = substitutor.replace(payload);
 
@@ -262,6 +265,30 @@ public  <T> T createPredictPayload(Map<String, String> parameters) {
         return (T) parameters.get("http_body");
     }
 
+    protected String fillNullParameters(Map<String, String> parameters, String payload) {
+        List<String> bodyParams = findStringParametersWithNullDefaultValue(payload);
+        String newPayload = payload;
+        for (String key : bodyParams) {
+            if (!parameters.containsKey(key) || parameters.get(key) == null) {
+                newPayload = newPayload.replace("\"${parameters." + key + ":-null}\"", "null");
+            }
+        }
+        return newPayload;
+    }
+
+    private List<String> findStringParametersWithNullDefaultValue(String input) {
+        String regex = "\"\\$\\{parameters\\.(\\w+):-null}\"";
+        Pattern pattern = Pattern.compile(regex);
+        Matcher matcher = pattern.matcher(input);
+
+        List<String> paramList = new ArrayList<>();
+        while (matcher.find()) {
+            String parameterValue = matcher.group(1);
+            paramList.add(parameterValue);
+        }
+        return paramList;
+    }
+
     @Override
     public void decrypt(Function<String, String> function) {
         Map<String, String> decrypted = new HashMap<>();
diff --git a/common/src/test/java/org/opensearch/ml/common/connector/HttpConnectorTest.java b/common/src/test/java/org/opensearch/ml/common/connector/HttpConnectorTest.java
index 1874791b8b..8e51a06c38 100644
--- a/common/src/test/java/org/opensearch/ml/common/connector/HttpConnectorTest.java
+++ b/common/src/test/java/org/opensearch/ml/common/connector/HttpConnectorTest.java
@@ -259,6 +259,14 @@ public void parseResponse_NonJsonString() throws IOException {
         Assert.assertEquals("test output", modelTensors.get(0).getDataAsMap().get("response"));
     }
 
+    @Test
+    public void fillNullParameters() {
+        HttpConnector connector = createHttpConnector();
+        Map<String, String> parameters = new HashMap<>();
+        String output = connector.fillNullParameters(parameters, "{\"input1\": \"${parameters.input1:-null}\"}");
+        Assert.assertEquals("{\"input1\": null}", output);
+    }
+
     public static HttpConnector createHttpConnector() {
         ConnectorAction.ActionType actionType = ConnectorAction.ActionType.PREDICT;
         String method = "POST";
diff --git a/ml-algorithms/src/main/java/org/opensearch/ml/engine/algorithms/remote/ConnectorUtils.java b/ml-algorithms/src/main/java/org/opensearch/ml/engine/algorithms/remote/ConnectorUtils.java
index 588da7ccae..cd3038f49c 100644
--- a/ml-algorithms/src/main/java/org/opensearch/ml/engine/algorithms/remote/ConnectorUtils.java
+++ b/ml-algorithms/src/main/java/org/opensearch/ml/engine/algorithms/remote/ConnectorUtils.java
@@ -99,7 +99,9 @@ public static RemoteInferenceInputDataSet processInput(MLInput mlInput, Connecto
         if (inputData.getParameters() != null) {
             Map<String, String> newParameters = new HashMap<>();
             inputData.getParameters().entrySet().forEach(entry -> {
-                if (StringUtils.isJson(entry.getValue())) {
+                if (entry.getValue() == null) {
+                    newParameters.put(entry.getKey(), entry.getValue());
+                } else if (StringUtils.isJson(entry.getValue())) {
                     // no need to escape if it's already valid json
                     newParameters.put(entry.getKey(), entry.getValue());
                 } else {
diff --git a/ml-algorithms/src/test/java/org/opensearch/ml/engine/algorithms/remote/ConnectorUtilsTest.java b/ml-algorithms/src/test/java/org/opensearch/ml/engine/algorithms/remote/ConnectorUtilsTest.java
index bfe5023b9a..2a84e2fee1 100644
--- a/ml-algorithms/src/test/java/org/opensearch/ml/engine/algorithms/remote/ConnectorUtilsTest.java
+++ b/ml-algorithms/src/test/java/org/opensearch/ml/engine/algorithms/remote/ConnectorUtilsTest.java
@@ -96,8 +96,16 @@ public void processInput_RemoteInferenceInputDataSet_NotEscapeJsonString() {
         processInput_RemoteInferenceInputDataSet(input, input);
     }
 
+    @Test
+    public void processInput_RemoteInferenceInputDataSet_NullParam() {
+        String input = null;
+        processInput_RemoteInferenceInputDataSet(input, input);
+    }
+
     private void processInput_RemoteInferenceInputDataSet(String input, String expectedInput) {
-        RemoteInferenceInputDataSet dataSet = RemoteInferenceInputDataSet.builder().parameters(ImmutableMap.of("input", input)).build();
+        Map<String, String> params = new HashMap<>();
+        params.put("input", input);
+        RemoteInferenceInputDataSet dataSet = RemoteInferenceInputDataSet.builder().parameters(params).build();
         MLInput mlInput = MLInput.builder().algorithm(FunctionName.REMOTE).inputDataset(dataSet).build();
 
         ConnectorAction predictAction = ConnectorAction.builder()