Incorporated pull request feedback:

* moved to jenkins.util.SystemProperties
* consistent naming getString/getInteger/getBoolean
* improved code formatting
Improved JavaDoc

core/src/main/java/hudson/LocalPluginManager.java

@@ -24,6 +24,7 @@
 
 package hudson;
 
+import jenkins.util.SystemProperties;
 import jenkins.model.Jenkins;
 
 import javax.servlet.ServletContext;
@@ -60,7 +61,7 @@ public class LocalPluginManager extends PluginManager {
     @Override
     protected Collection<String> loadBundledPlugins() {
         // this is used in tests, when we want to override the default bundled plugins with .jpl (or .hpl) versions
-        if (SystemProperties.getProperty("hudson.bundled.plugins") != null) {
+        if (SystemProperties.getString("hudson.bundled.plugins") != null) {
             return Collections.emptySet();
         }