Investigate Null Arg Exception on Export

[aMytho]

Some PDFs throw a null arg exception when the PDF is saved. This mostly seems to occur on PDF versions older than 1.5.

I can make some of them work in a blank iText project, but others don't work at all.

One possibility is document corruption. However, those that work in a normal iText project would not have that issue. It might be something with the way we use streams to load the PDF reader/writer.