The XmlStructFactory class  can generate invalid ProductType objects if an XML product-types.xml file has policy missing either the "<metadata/>" tag or the "<metExtractors/>" tag. Moreover, if these nodes are missing, the user is not informed about the missing elements and is instead presented with a NullPointerException when new policy is written automatically via the AddProductTypeCliAction (or other such tools).
I propose the following:
- XmlStructFactory's getProductType method should NOT default the initialization of the met (Metadata) object or the extractors (List<ExtractorSpec>) object to be null. Instead, they should be initialized as an empty Metadata object and an empty Vector<ExtractorSpec> list respectively.
- XmlStructFactory's getProductType method should warn the user via a Logger warning that either a "<metadata/>" or "<metExtractors/>" node is missing
The reason I propose we default the metadata and metExtractors object to be empty objects instead of null objects, is because of the way the ProductType  object constructor is configured. By default, instantiating a new ProductType object leads its internal Metadata and metExtractors objects being set to empty objects instead of null objects. However, through the XmlStructFactory, this pattern breaks when a metadata or metExtractors node is not present in policy - these objects are set to null and the new ProductType that is generated on line 202 of XmlStructFactory is corrupted. This can be prevented by a simple initialization change as proposed.