RATIS-2129. Single call of getLastTermIndex

Author: symious

ratis-server/src/main/java/org/apache/ratis/server/raftlog/segmented/SegmentedRaftLogCache.java

@@ -614,10 +614,12 @@ long getLastIndexInClosedSegments() {
 
   TermIndex getLastTermIndex() {
     try (AutoCloseableLock readLock = closedSegments.readLock()) {
-      return (openSegment != null && openSegment.getLastTermIndex() != null) ?
-          openSegment.getLastTermIndex() :
-          (closedSegments.isEmpty() ? null :
-              closedSegments.get(closedSegments.size() - 1).getLastTermIndex());
+      TermIndex lastOpenIndex =
+          (openSegment != null) ? openSegment.getLastTermIndex() : null;
+      return lastOpenIndex != null
+          ? lastOpenIndex
+          : (closedSegments.isEmpty() ? null :
+          closedSegments.get(closedSegments.size() - 1).getLastTermIndex());
     }
   }