minor refactoring according to the comments

application/src/main/java/org/thingsboard/server/service/apiusage/DefaultTbApiUsageStateService.java

@@ -153,7 +153,7 @@ public class DefaultTbApiUsageStateService extends AbstractPartitionBasedService
         List<TransportProtos.UsageStatsServiceMsg> msgs;
 
         //For backward compatibility, remove after release
-        if (serviceMsg.getTenantIdMSB() != 0) {
+        if (serviceMsg.getMsgsList().isEmpty()) {
             TransportProtos.UsageStatsServiceMsg oldMsg = TransportProtos.UsageStatsServiceMsg.newBuilder()
                     .setTenantIdMSB(serviceMsg.getTenantIdMSB())
                     .setTenantIdLSB(serviceMsg.getTenantIdLSB())
@@ -211,7 +211,7 @@ public class DefaultTbApiUsageStateService extends AbstractPartitionBasedService
                 if (StringUtils.isNotEmpty(statsItem.getKey())) {
                     recordKey = ApiUsageRecordKey.valueOf(statsItem.getKey());
                 } else {
-                    recordKey = ProtoUtils.fromProto(statsItem.getKeyProto());
+                    recordKey = ProtoUtils.fromProto(statsItem.getRecordKey());
                 }
 
                 StatsCalculationResult calculationResult = usageState.calculate(recordKey, statsItem.getValue(), serviceId);

common/proto/src/main/proto/queue.proto

@@ -1737,7 +1737,7 @@ message ToTransportMsg {
 message UsageStatsKVProto {
   string key = 1 [deprecated=true];
   int64 value = 2;
-  ApiUsageRecordKeyProto keyProto = 3;
+  ApiUsageRecordKeyProto recordKey = 3;
 }
 
 message ToUsageStatsServiceMsg {

common/queue/src/main/java/org/thingsboard/server/queue/usagestats/DefaultTbApiUsageReportClient.java

@@ -119,7 +119,7 @@ public class DefaultTbApiUsageReportClient implements TbApiUsageReportClient {
                 });
 
                 UsageStatsKVProto.Builder statsItem = UsageStatsKVProto.newBuilder()
-                        .setKeyProto(ProtoUtils.toProto(key))
+                        .setRecordKey(ProtoUtils.toProto(key))
                         .setValue(value);
                 statsMsg.addValues(statsItem.build());
             });