doc improvement.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@5634 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/model/JobPropertyDescriptor.java

 package hudson.model;
 
+import org.kohsuke.stapler.StaplerRequest;
+
 import java.util.List;
 import java.util.ArrayList;
 
+import net.sf.json.JSONObject;
+
 /**
  * {@link Descriptor} for {@link JobProperty}.
  * 
@@ -15,6 +19,16 @@ public abstract class JobPropertyDescriptor extends Descriptor<JobProperty<?>> {
         super(clazz);
     }
 
+    /**
+     * {@inheritDoc}
+     *
+     * @return
+     *      null to avoid setting an instance of {@link JobProperty} to the target project.
+     */
+    public JobProperty<?> newInstance(StaplerRequest req, JSONObject formData) throws FormException {
+        return super.newInstance(req, formData);
+    }
+
     /**
      * Returns true if this {@link JobProperty} type is applicable to the
      * given job type.