diff --git a/client/transport/jsonrpc/src/test/java/org/a2aproject/sdk/client/transport/jsonrpc/JSONRPCTransportTest.java b/client/transport/jsonrpc/src/test/java/org/a2aproject/sdk/client/transport/jsonrpc/JSONRPCTransportTest.java
index 5349c4753..855c49611 100644
--- a/client/transport/jsonrpc/src/test/java/org/a2aproject/sdk/client/transport/jsonrpc/JSONRPCTransportTest.java
+++ b/client/transport/jsonrpc/src/test/java/org/a2aproject/sdk/client/transport/jsonrpc/JSONRPCTransportTest.java
@@ -97,14 +97,14 @@ public void tearDown() {
     public void testListTasksWithDefaultBuilder() throws Exception {
         JsonObject params = listTasksAndGetRequestParams(ListTasksParams.builder().build());
 
-        assertEquals("", params.get("tenant").getAsString());
+        assertFalse(params.has("tenant"));
     }
 
     @Test
     public void testListTasksWithDefaultConstructor() throws Exception {
         JsonObject params = listTasksAndGetRequestParams(new ListTasksParams());
 
-        assertEquals("", params.get("tenant").getAsString());
+        assertFalse(params.has("tenant"));
     }
 
     @Test
diff --git a/client/transport/jsonrpc/src/test/java/org/a2aproject/sdk/client/transport/jsonrpc/JsonMessages.java b/client/transport/jsonrpc/src/test/java/org/a2aproject/sdk/client/transport/jsonrpc/JsonMessages.java
index f73e9d8ed..aba7703d7 100644
--- a/client/transport/jsonrpc/src/test/java/org/a2aproject/sdk/client/transport/jsonrpc/JsonMessages.java
+++ b/client/transport/jsonrpc/src/test/java/org/a2aproject/sdk/client/transport/jsonrpc/JsonMessages.java
@@ -150,8 +150,7 @@ public class JsonMessages {
             "configuration":{
               "acceptedOutputModes":[
                 "text"
-              ],
-              "returnImmediately":false
+              ]
             },
             "metadata":{
 
@@ -200,8 +199,7 @@ public class JsonMessages {
                 "configuration":{
                   "acceptedOutputModes":[
                     "text"
-                  ],
-                  "returnImmediately":false
+                  ]
                 },
                 "metadata":{
                   
@@ -384,8 +382,7 @@ public class JsonMessages {
                  "configuration":{
                    "acceptedOutputModes":[
                      "text"
-                   ],
-                   "returnImmediately":false
+                   ]
                  },
                  "metadata":{
                    
@@ -451,8 +448,7 @@ public class JsonMessages {
                 "configuration":{
                   "acceptedOutputModes":[
                     "text"
-                  ],
-                  "returnImmediately":false
+                  ]
                 },
                 "metadata":{
                   
@@ -522,8 +518,7 @@ public class JsonMessages {
                 "configuration":{
                   "acceptedOutputModes":[
                     "text"
-                  ],
-                  "returnImmediately":false
+                  ]
                 },
                 "metadata":{
                   
diff --git a/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/utils/JSONRPCUtils.java b/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/utils/JSONRPCUtils.java
index 89cb05c9b..0e9e7bf8b 100644
--- a/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/utils/JSONRPCUtils.java
+++ b/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/utils/JSONRPCUtils.java
@@ -581,8 +581,9 @@ public static String toJsonRPCRequest(@Nullable String requestId, String method,
                 output.name("method").value(method);
             }
             if (payload != null) {
+                // Unlike responses, omit unset fields: receivers may treat "taskId": "" as a real value
                 String resultValue = ProtoJsonUtils.toJson(
-                        JsonFormat.printer().alwaysPrintFieldsWithNoPresence().omittingInsignificantWhitespace(), payload);
+                        JsonFormat.printer().omittingInsignificantWhitespace(), payload);
                 output.name("params").jsonValue(resultValue);
             }
             output.endObject();
diff --git a/spec-grpc/src/test/java/org/a2aproject/sdk/grpc/utils/JSONRPCUtilsTest.java b/spec-grpc/src/test/java/org/a2aproject/sdk/grpc/utils/JSONRPCUtilsTest.java
index fcead19af..c7f166588 100644
--- a/spec-grpc/src/test/java/org/a2aproject/sdk/grpc/utils/JSONRPCUtilsTest.java
+++ b/spec-grpc/src/test/java/org/a2aproject/sdk/grpc/utils/JSONRPCUtilsTest.java
@@ -762,6 +762,32 @@ public void testToJsonRPCRequest_doesNotHtmlEscapeAngleBrackets() {
             "JSON must not contain HTML-escaped '>' (\\u003e) but got: " + json);
     }
 
+    @Test
+    public void testToJsonRPCRequest_omitsUnsetFields() throws JsonProcessingException {
+        // Issue #770: unset taskId, contextId and tenant were sent as empty strings
+        MessageSendParams params = new MessageSendParams(
+            Message.builder()
+                .role(Message.Role.ROLE_USER)
+                .parts(Collections.singletonList(new TextPart("hello")))
+                .messageId("message-1234")
+                .build(),
+            null, null
+        );
+
+        String json = JSONRPCUtils.toJsonRPCRequest("test-id", SEND_MESSAGE_METHOD,
+            ProtoUtils.ToProto.sendMessageRequest(params));
+
+        JsonObject requestParams = JsonParser.parseString(json).getAsJsonObject().getAsJsonObject("params");
+        assertFalse(requestParams.has("tenant"), json);
+        JsonObject message = requestParams.getAsJsonObject("message");
+        assertFalse(message.has("taskId"), json);
+        assertFalse(message.has("contextId"), json);
+        Message parsed = assertInstanceOf(SendMessageRequest.class, JSONRPCUtils.parseRequestBody(json, null))
+            .getParams().message();
+        assertNull(parsed.taskId());
+        assertNull(parsed.contextId());
+    }
+
     @Test
     public void testToJsonRPCResultResponse_doesNotHtmlEscapeAngleBrackets() {
         // Reproduce issue #892: server responses must also send literal angle brackets.