title: iText7 (PdfSweep): NullPointerException on redacting text
body: <p>I am trying to edit the text from PDF using PDFSweep 2.0.0 (JAVA). I used <a href="https://developers.itextpdf.com/examples/content-extraction-and-redaction/clone-removing-content/customizing-redaction-pdfsweep" rel="nofollow noreferrer">this example</a>. </p>
  
  <p>It works for most of the PDFs I have, but on some PDF files, the code throws <code>NullPointerException</code>. </p>
  
  <p>Here is code sample:</p>
  
  <pre><code>    CompositeCleanupStrategy strategy = new CompositeCleanupStrategy();
      strategy.add(new CustomLocationExtractionStrategy("Joe"));
  
      PdfDocument pdf = new PdfDocument(new PdfReader(SRC), new PdfWriter(DEST));
  
      // sweep
      PdfAutoSweep autoSweep = new PdfAutoSweep(strategy);
      autoSweep.cleanUp(pdf);
      pdf.close();
  </code></pre>
  
  <p>I used <a href="https://drive.google.com/open?id=1jw-fX5Rh7C7K9gdu4p-Ot4GbpAUKmbMX" rel="nofollow noreferrer">this PDF</a> as SRC file. Is this a bug of itext7/pdfsweep?</p>