rely on try-with-resources

core/src/main/java/hudson/PluginWrapper.java

@@ -708,11 +708,8 @@ public class PluginWrapper implements Comparable<PluginWrapper>, ModelObject {
         File backup = getBackupFile();
         if (backup.exists()) {
             try {
-                JarFile backupPlugin = new JarFile(backup);
-                try {
+                try (JarFile backupPlugin = new JarFile(backup)) {
                     return backupPlugin.getManifest().getMainAttributes().getValue("Plugin-Version");
-                } finally {
-                    backupPlugin.close();
                 }
             } catch (IOException e) {
                 LOGGER.log(WARNING, "Failed to get backup version from " + backup, e);