#151 Selecting section of mparticle as Related Link causes NPE

[Terry]

Steps to reproduce:

1. Edit existing article
2. Go to Authoring > Related Links
3. Tick "Content Item" and click Search
4. Click Search tab
5. Enter a query that will return an Article Section
6. Select item for a matching section
7. Click Create
8. Exception is reported:

java.lang.NullPointerException
at com.arsdigita.cms.contenttypes.Link.getInternalOrExternalURI(Link.java:294)
at com.arsdigita.cms.contenttypes.ui.LinkTable$LinkTableRenderer.getComponent(LinkTable.java:154)
at com.arsdigita.bebop.Table.generateXML(Table.java:738)

Problem:

ArticleSection doesn't have a parent_id in CMS_ITEMS table. Could have fixed this but then need data conversion to populate the existing records. An easier fix is to invoke getMPArticle() instead of getParent() in ArticleSection.getContentSection().

[Terry]

Simple patch to ArticleSection