fixed pr comments

application/src/main/java/org/thingsboard/server/service/queue/DefaultTbCoreConsumerService.java

@@ -465,8 +465,8 @@ public class DefaultTbCoreConsumerService extends AbstractConsumerService<ToCore
         return firmwareStateService.process(msg.getValue());
     }
 
-    private void forwardToCoreRpcService(FromDeviceRPCResponseProto proto, TbCallback callback) {
-        RpcError error = proto.getError() >= 0 ? RpcError.values()[proto.getError()] : null;
+    void forwardToCoreRpcService(FromDeviceRPCResponseProto proto, TbCallback callback) {
+        RpcError error = RpcError.fromProtoErrorCode(proto.getError());
         FromDeviceRpcResponse response = new FromDeviceRpcResponse(new UUID(proto.getRequestIdMSB(), proto.getRequestIdLSB())
                 , proto.hasResponse() ? proto.getResponse() : null, error);
         tbCoreDeviceRpcService.processRpcResponseFromRuleEngine(response);

application/src/main/java/org/thingsboard/server/service/queue/DefaultTbRuleEngineConsumerService.java

@@ -180,7 +180,7 @@ public class DefaultTbRuleEngineConsumerService extends AbstractPartitionBasedCo
             callback.onSuccess();
         } else if (nfMsg.hasFromDeviceRpcResponse()) {
             TransportProtos.FromDeviceRPCResponseProto proto = nfMsg.getFromDeviceRpcResponse();
-            RpcError error = proto.getError() >= 0 ? RpcError.values()[proto.getError()] : null;
+            RpcError error = RpcError.fromProtoErrorCode(proto.getError());
             FromDeviceRpcResponse response = new FromDeviceRpcResponse(new UUID(proto.getRequestIdMSB(), proto.getRequestIdLSB())
                     , proto.hasResponse() ? proto.getResponse() : null, error);
             tbDeviceRpcService.processRpcResponseFromDevice(response);

application/src/test/java/org/thingsboard/server/service/queue/DefaultTbCoreConsumerServiceTest.java

@@ -27,8 +27,11 @@ import org.mockito.junit.jupiter.MockitoExtension;
 import org.springframework.test.util.ReflectionTestUtils;
 import org.thingsboard.server.common.data.id.DeviceId;
 import org.thingsboard.server.common.data.id.TenantId;
+import org.thingsboard.server.common.data.rpc.RpcError;
 import org.thingsboard.server.common.msg.queue.TbCallback;
+import org.thingsboard.server.common.msg.rpc.FromDeviceRpcResponse;
 import org.thingsboard.server.gen.transport.TransportProtos;
+import org.thingsboard.server.service.rpc.TbCoreDeviceRpcService;
 import org.thingsboard.server.service.ruleengine.RuleEngineCallService;
 import org.thingsboard.server.service.state.DeviceStateService;
 
@@ -51,6 +54,8 @@ public class DefaultTbCoreConsumerServiceTest {
     private TbCoreConsumerStats statsMock;
     @Mock
     private RuleEngineCallService ruleEngineCallServiceMock;
+    @Mock
+    private TbCoreDeviceRpcService tbCoreDeviceRpcServiceMock;
 
     @Mock
     private TbCallback tbCallbackMock;
@@ -638,4 +643,31 @@ public class DefaultTbCoreConsumerServiceTest {
         then(ruleEngineCallServiceMock).should().onQueueMsg(restApiCallResponseMsgProto, tbCallbackMock);
     }
 
+    @Test
+    public void givenNotFoundErrorAndNoResponse_whenForwardToCoreRpcService_thenNotFoundAndNullResponseAreRecovered() {
+        // GIVEN
+        ReflectionTestUtils.setField(defaultTbCoreConsumerServiceMock, "tbCoreDeviceRpcService", tbCoreDeviceRpcServiceMock);
+        var requestId = UUID.randomUUID();
+        // error = NOT_FOUND.ordinal() (0) and response left unset: the previously broken combination
+        // ('error > 0' dropped NOT_FOUND, proto3 default collapsed a null response to "").
+        var proto = TransportProtos.FromDeviceRPCResponseProto.newBuilder()
+                .setRequestIdMSB(requestId.getMostSignificantBits())
+                .setRequestIdLSB(requestId.getLeastSignificantBits())
+                .setError(RpcError.NOT_FOUND.ordinal())
+                .build();
+        doCallRealMethod().when(defaultTbCoreConsumerServiceMock).forwardToCoreRpcService(proto, tbCallbackMock);
+
+        // WHEN
+        defaultTbCoreConsumerServiceMock.forwardToCoreRpcService(proto, tbCallbackMock);
+
+        // THEN
+        var responseCaptor = ArgumentCaptor.forClass(FromDeviceRpcResponse.class);
+        then(tbCoreDeviceRpcServiceMock).should().processRpcResponseFromRuleEngine(responseCaptor.capture());
+        var response = responseCaptor.getValue();
+        assertThat(response.getId()).isEqualTo(requestId);
+        assertThat(response.getError()).contains(RpcError.NOT_FOUND);
+        assertThat(response.getResponse()).isEmpty();
+        then(tbCallbackMock).should().onSuccess();
+    }
+
 }

application/src/test/java/org/thingsboard/server/service/queue/DefaultTbRuleEngineConsumerServiceTest.java

@@ -0,0 +1,78 @@
+/**
+ * Copyright © 2016-2026 The Thingsboard Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.thingsboard.server.service.queue;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.ArgumentCaptor;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.springframework.test.util.ReflectionTestUtils;
+import org.thingsboard.server.common.data.rpc.RpcError;
+import org.thingsboard.server.common.msg.queue.TbCallback;
+import org.thingsboard.server.common.msg.rpc.FromDeviceRpcResponse;
+import org.thingsboard.server.gen.transport.TransportProtos;
+import org.thingsboard.server.gen.transport.TransportProtos.ToRuleEngineNotificationMsg;
+import org.thingsboard.server.queue.common.TbProtoQueueMsg;
+import org.thingsboard.server.service.rpc.TbRuleEngineDeviceRpcService;
+
+import java.util.UUID;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.BDDMockito.then;
+import static org.mockito.Mockito.doCallRealMethod;
+
+@ExtendWith(MockitoExtension.class)
+public class DefaultTbRuleEngineConsumerServiceTest {
+
+    @Mock
+    private TbRuleEngineDeviceRpcService tbDeviceRpcServiceMock;
+    @Mock
+    private TbCallback tbCallbackMock;
+
+    @Mock
+    private DefaultTbRuleEngineConsumerService defaultTbRuleEngineConsumerServiceMock;
+
+    @Test
+    public void givenNotFoundErrorAndNoResponse_whenHandleFromDeviceRpcResponse_thenNotFoundAndNullResponseAreRecovered() {
+        // GIVEN
+        ReflectionTestUtils.setField(defaultTbRuleEngineConsumerServiceMock, "tbDeviceRpcService", tbDeviceRpcServiceMock);
+        var requestId = UUID.randomUUID();
+        // error = NOT_FOUND.ordinal() (0) and response left unset: the previously broken combination
+        // ('error > 0' dropped NOT_FOUND, proto3 default collapsed a null response to "").
+        var proto = TransportProtos.FromDeviceRPCResponseProto.newBuilder()
+                .setRequestIdMSB(requestId.getMostSignificantBits())
+                .setRequestIdLSB(requestId.getLeastSignificantBits())
+                .setError(RpcError.NOT_FOUND.ordinal())
+                .build();
+        var nfMsg = ToRuleEngineNotificationMsg.newBuilder().setFromDeviceRpcResponse(proto).build();
+        var queueMsg = new TbProtoQueueMsg<>(requestId, nfMsg);
+        doCallRealMethod().when(defaultTbRuleEngineConsumerServiceMock).handleNotification(requestId, queueMsg, tbCallbackMock);
+
+        // WHEN
+        defaultTbRuleEngineConsumerServiceMock.handleNotification(requestId, queueMsg, tbCallbackMock);
+
+        // THEN
+        var responseCaptor = ArgumentCaptor.forClass(FromDeviceRpcResponse.class);
+        then(tbDeviceRpcServiceMock).should().processRpcResponseFromDevice(responseCaptor.capture());
+        var response = responseCaptor.getValue();
+        assertThat(response.getId()).isEqualTo(requestId);
+        assertThat(response.getError()).contains(RpcError.NOT_FOUND);
+        assertThat(response.getResponse()).isEmpty();
+        then(tbCallbackMock).should().onSuccess();
+    }
+
+}

common/data/src/main/java/org/thingsboard/server/common/data/rpc/RpcError.java

@@ -20,4 +20,16 @@ package org.thingsboard.server.common.data.rpc;
  */
 public enum RpcError {
     NOT_FOUND, FORBIDDEN, NO_ACTIVE_CONNECTION, TIMEOUT, INTERNAL;
+
+    private static final RpcError[] VALUES = values();
+
+    /**
+     * Resolves an {@link RpcError} from the proto {@code error} ordinal.
+     * Returns {@code null} both for the "no error" sentinel (negative value) and for unknown ordinals
+     * that a newer node in a mixed-version cluster might emit, so callers never hit an
+     * {@link ArrayIndexOutOfBoundsException}.
+     */
+    public static RpcError fromProtoErrorCode(int errorCode) {
+        return errorCode >= 0 && errorCode < VALUES.length ? VALUES[errorCode] : null;
+    }
 }

common/proto/src/main/java/org/thingsboard/server/common/util/ProtoUtils.java

@@ -587,7 +587,7 @@ public class ProtoUtils {
         FromDeviceRpcResponse fromDeviceRpcResponse = new FromDeviceRpcResponse(
                 new UUID(rpcResponse.getRequestIdMSB(), rpcResponse.getRequestIdLSB()),
                 rpcResponse.hasResponse() ? rpcResponse.getResponse() : null,
-                rpcResponse.getError() >= 0 ? RpcError.values()[rpcResponse.getError()] : null);
+                RpcError.fromProtoErrorCode(rpcResponse.getError()));
         return new FromDeviceRpcResponseActorMsg(
                 proto.getRequestId(),
                 TenantId.fromUUID(new UUID(proto.getTenantIdMSB(), proto.getTenantIdLSB())),