make sure entry is not null

Author: vladak

opengrok-web/src/main/webapp/history.jsp

@@ -258,12 +258,14 @@ document.domReady.push(function() {domReadyHistory();});
             <%
             int count=0;
             for (HistoryEntry entry : hist.getHistoryEntries(maxItems, startIndex)) {
-                final String dispRev = Optional.ofNullable(entry).
-                        map(HistoryEntry::getDisplayRevision).
+                if (Objects.isNull(entry)) {
+                    continue;
+                }
+
+                final String dispRev = Optional.ofNullable(entry.getDisplayRevision()).
                         map(Util::htmlize).
                         orElse("");
-                final String rev = Optional.ofNullable(entry).
-                        map(HistoryEntry::getRevision).
+                final String rev = Optional.ofNullable(entry.getRevision()).
                         orElse("");
 
                 String tags = hist.getTags().get(rev);