If you create a PDF document from org.apache.pdfbox.TextToPDF like so:
TextToPDF pdfCreator = new TextToPDF();
PDDocument pdfDoc = pdfCreator.createPDFFromText(new StringReader("")); // Note the empty String
then it does produce a PDF file. But the file cannot be opened as it contains no pages.
Adobe Reader (I have 9.4.1), and Mac OSX's Preview/Quicklook cannot open the document.
I have attached (or will do in a minute) a patch that includes a test case that reproduces the problem (no PDPages in a PDF with no text).
And I've patched TextToPDF so that it inserts a single empty page for an empty string input.