Now the exception can be obtained only in struts-config.xml, but faults in our code make it probable to appear more generally.

EXECUTE: Create Struts KickStart project and open struts-config.xml
EXECUTE: Create global exception

  <exception className="/pages/greeting.jsp" key="a" path="/greeting.do" type="b"/>

where 'className' is deliberately assigned to an existing page path instead of a class name.
EXECUTE: Call open-on options over word 'greeting'
ASSERT: Two options appear:
1) open class 'greeting.jsp'
2) Open '/struts/WebContent/pages/greeting.jsp' with JBoss Tools JSP Editor
EXECUTE: Call open-on options over symbol '/'
FAILURE: null pointer exception; two options may still appear:
1) empty label
2) Open '/struts/WebContent/pages/greeting.jsp' with JBoss Tools JSP Editor

I see the cause of the exception in difference of algorithm computing class name region in classes XMLClassHyperlinkPartitioner and ClassHyperlink. Partitioner returns attribute value with trimmed white spaces ant quote symbols. So, even if open-on is invoked over '/', partitioner reports XML_CLASS region and instance of ClassHyperlink is created for it. But ClassHyperlink computes region more strictly, so that text contains only qualified Java name symbols. When open-on is invoked over '/', ClassHyperlink sets region to open to null. If there is no other hyperlink option, that may pass, but when several hyperlinks are detected, MultipleHyperlinkPresenter requests each for hyperlink text, and ClassHyperlink fails. In this case the other option is WST's WorkspaceFileHyperlink, it detects in any attribute values resource paths; if it starts to detect them in text nodes (and why not?), this issue will take place in faces-config.xml and web.xml, where class names are assigned as text nodes.

This issue cannot be fixed just by preventing NPE, because open-on option with empty label may appear all the same. Solution is to let partitioner report a region for a corresponding hyperlink only when the hyperlink accepts that region as relevant.