Minor refactorings either for performance or readability (#4845)

Co-authored-by: Oleg Nenashev <o.v.nenashev@gmail.com>

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

@@ -221,7 +221,7 @@ public class PluginWrapper implements Comparable<PluginWrapper>, ModelObject {
      * The core can depend on a plugin if it is bundled. Sometimes it's the only thing that
      * depends on the plugin e.g. UI support library bundle plugin.
      */
-    private static Set<String> CORE_ONLY_DEPENDANT = ImmutableSet.copyOf(Arrays.asList("jenkins-core"));
+    private static Set<String> CORE_ONLY_DEPENDANT = ImmutableSet.copyOf(Collections.singletonList("jenkins-core"));
 
     /**
      * Set the list of components that depend on this plugin.