NullPointerException in JcrNodeDefinition.ensureRequiredPrimaryTypesLoaded()

Using the attached CND file, the repository set-up fails with an NPE when attempting to resolve node types. (ala config.repository(xxxxxx).addNodeTypes('test_cnd.cnd')

java.lang.NullPointerException
at org.jboss.dna.jcr.JcrNodeDefinition.ensureRequiredPrimaryTypesLoaded(JcrNodeDefinition.java:113)
at org.jboss.dna.jcr.JcrNodeDefinition.getRequiredPrimaryTypes(JcrNodeDefinition.java:161)
at org.jboss.dna.jcr.RepositoryNodeTypeManager.validate(RepositoryNodeTypeManager.java:1938)
at org.jboss.dna.jcr.RepositoryNodeTypeManager.validate(RepositoryNodeTypeManager.java:1861)
at org.jboss.dna.jcr.RepositoryNodeTypeManager.registerNodeTypes(RepositoryNodeTypeManager.java:1513)
at org.jboss.dna.jcr.JcrEngine.doCreateJcrRepository(JcrEngine.java:246)
at org.jboss.dna.jcr.JcrEngine.getRepository(JcrEngine.java:161)

My original DDL seqencer cnd is much more complex, but by paring it down to the following, the error still occured.

//------------------------------------------------------------------------------
// N A M E S P A C E S
//------------------------------------------------------------------------------
<jcr='http://www.jcp.org/jcr/1.0'>
<nt='http://www.jcp.org/jcr/nt/1.0'>
<mix='http://www.jcp.org/jcr/mix/1.0'>
<ddl='http://jboss.org/dna/ddl/1.0'>

[ddl:statement] mixin abstract

• ddl:expression (string) mandatory
  + * (ddl:ddlProblem) = ddl:ddlProblem multiple

[ddl:schemaDefinition] > ddl:statement mixin

• ddl:defaultCharacterSetName (STRING)
  + * (ddl:ddlStatement) = ddl:ddlStatement multiple

[ddl:ddlProblem] mixin

• ddl:problemLevel (LONG) mandatory
• ddl:message (STRING) mandatory

The [ddl:schemaDefinition] mixin is the ONLY mixin that both extends a mixin and allows children of the same mixin type (i.e. [ddl:statement]) however the NPE is occuring when attempting to find the primary node type for [ddl:ddlProblem]

Note that the NPE does not occur when the [ddl:schemaDefinition] type is removed.