dcache-bulk: small improvement to RB 13915

Motivation:

Reduce number of conditional checks in fix #13915.

Modification:

Use single if-else and `optString`.

Result:

Code less verbose and "more efficient".

Target: master
Request: 8.2
Patch: https://rb.dcache.org/r/13916/
Requires-notes: no
Acked-by: Dmitry
Committed: master@
Pull-request:  cherry-picked to #7047

modules/dcache-bulk/src/main/java/org/dcache/services/bulk/activity/plugin/pin/StageActivity.java

@@ -152,17 +152,8 @@ private ProtocolInfo getProtocolInfo() throws URISyntaxException {
     }
 
     private long getLifetimeInMillis(FsPath path) {
-        String ptString = null;
-
-        String key = path.toString();
-
-        if (jsonLifetimes != null && jsonLifetimes.has(key)) {
-            ptString = jsonLifetimes.getString(key);
-        }
-
-        if (ptString == null) {
-            ptString = DISK_LIFETIME.getDefaultValue();
-        }
+        String ptString = jsonLifetimes == null ? DISK_LIFETIME.getDefaultValue()
+              : jsonLifetimes.optString(path.toString(), DISK_LIFETIME.getDefaultValue());
 
         return TimeUnit.SECONDS.toMillis(Duration.parse(ptString).get(ChronoUnit.SECONDS));
     }