Null values support for subscription update values proto

@@ -492,12 +492,14 @@ public class DefaultSubscriptionManagerService extends TbApplicationEventListene
             boolean hasData = false;
             for (Object v : value) {
                 Object[] array = (Object[]) v;
-                dataBuilder.addTs((long) array[0]);
+                TbSubscriptionUpdateTsValue.Builder tsValueBuilder = TbSubscriptionUpdateTsValue.newBuilder();
+                tsValueBuilder.setTs((long) array[0]);
                 String strVal = (String) array[1];
                 if (strVal != null) {
                     hasData = true;
-                    dataBuilder.addValue(strVal);
+                    tsValueBuilder.setValue(strVal);
                 }
+                dataBuilder.addTsValue(tsValueBuilder.build());
             }
             if (!ignoreEmptyUpdates || hasData) {
                 builder.addData(dataBuilder.build());

@@ -42,6 +42,7 @@ import org.thingsboard.server.gen.transport.TransportProtos.TbSubscriptionCloseP
 import org.thingsboard.server.gen.transport.TransportProtos.TbSubscriptionKetStateProto;
 import org.thingsboard.server.gen.transport.TransportProtos.TbSubscriptionProto;
 import org.thingsboard.server.gen.transport.TransportProtos.TbSubscriptionUpdateProto;
+import org.thingsboard.server.gen.transport.TransportProtos.TbSubscriptionUpdateTsValue;
 import org.thingsboard.server.gen.transport.TransportProtos.TbTimeSeriesSubscriptionProto;
 import org.thingsboard.server.gen.transport.TransportProtos.TbTimeSeriesUpdateProto;
 import org.thingsboard.server.gen.transport.TransportProtos.ToCoreMsg;
@@ -171,10 +172,11 @@ public class TbSubscriptionUtils {
             Map<String, List<Object>> data = new TreeMap<>();
             proto.getDataList().forEach(v -> {
                 List<Object> values = data.computeIfAbsent(v.getKey(), k -> new ArrayList<>());
-                for (int i = 0; i < v.getTsCount(); i++) {
+                for (int i = 0; i < v.getTsValueCount(); i++) {
                     Object[] value = new Object[2];
-                    value[0] = v.getTs(i);
-                    value[1] = v.getValue(i);
+                    TbSubscriptionUpdateTsValue tsValue = v.getTsValue(i);
+                    value[0] = tsValue.getTs();
+                    value[1] = tsValue.hasValue() ? tsValue.getValue() : null;
                     values.add(value);
                 }
             });

@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 syntax = "proto3";
+
 package transport;
 
 option java_package = "org.thingsboard.server.gen.transport";
@@ -581,8 +582,12 @@ message TbSubscriptionKetStateProto {
 
 message TbSubscriptionUpdateValueListProto {
   string key = 1;
-  repeated int64 ts = 2;
-  repeated string value = 3;
+  repeated TbSubscriptionUpdateTsValue tsValue = 2;
+}
+
+message TbSubscriptionUpdateTsValue {
+   int64 ts = 1;
+   optional string value = 2;
 }
 
 /**