Uncaught TypeError: Cannot set property 'value' of null

Refers to line 1124 of pdf-viewer.tpl.php: document.getElementById('fileInput').value = null;

Here is the whole code block:

if (PDFJS.isFirefoxExtension || !window.File || !window.FileReader ||
      !window.FileList || !window.Blob) {
    document.getElementById('fileInput').setAttribute('hidden', 'true');
    document.getElementById('fileInputSeperator')
                              .setAttribute('hidden', 'true');
  } else {
    document.getElementById('fileInput').value = null;
  }

I set up my installation by cloning the pdf.js git repo and running the 'make' command.