ReindexDataStreamIndex bug in assertion caused by reference equality (elastic#121325)

Assertion was using reference equality on two boxed longs. So assertion could produce false positives. Change to Objects.equals to check value and avoid null check.

(cherry picked from commit eeb745c)

Author: parkertimmins

docs/changelog/121325.yaml

@@ -0,0 +1,5 @@
+pr: 121325
+summary: '`ReindexDataStreamIndex` bug in assertion caused by reference equality'
+area: Data streams
+type: bug
+issues: []

x-pack/plugin/migrate/src/main/java/org/elasticsearch/xpack/migrate/action/ReindexDataStreamIndexTransportAction.java

@@ -54,6 +54,7 @@
 
 import java.util.Locale;
 import java.util.Map;
+import java.util.Objects;
 
 import static org.elasticsearch.cluster.metadata.IndexMetadata.APIBlock.WRITE;
 
@@ -372,7 +373,7 @@ private void sanityCheck(
                 listener.delegateFailureAndWrap((delegate, ignored) -> {
                     getIndexDocCount(sourceIndexName, parentTaskId, delegate.delegateFailureAndWrap((delegate1, sourceCount) -> {
                         getIndexDocCount(destIndexName, parentTaskId, delegate1.delegateFailureAndWrap((delegate2, destCount) -> {
-                            assert sourceCount == destCount
+                            assert Objects.equals(sourceCount, destCount)
                                 : String.format(
                                     Locale.ROOT,
                                     "source index [%s] has %d docs and dest [%s] has %d docs",