Hi Jason,
I've noticed a strange behavior for the first time, when you extract a docx file and open the numbering.xml, I found that for a certain document that some of the "w:abstractNum" tags are empty, i.e the tag does not contain any "w:lvl" tags. This reflects in a NullPointer exception in the constructor of "ListNumberingDefinition".
What happens is, in the method "initialiseMaps" in class "NumberingDefinitionsPart", there is a loop looping on the HashMap of ...