According to the spec, when parsing a cross reference stream and the W array has a 0 as first element (something like [0 4 1]). this should happen:
"If the first element is zero, the type field shall not be present, and shall default to type 1".
So entries read in this scenario should have type 1, in use.
From org.apache.pdfbox.pdfparser.PDFXrefStreamParser::parse line 115-123 the default type assigned by PDFBox in this scenario is 0, free.