app.doScript error on line 41

Hi! I'm trying to write a script for InDesign but there is an error on line 41 (right at the end): it says 'undefined' is not an object. Can someone helpe me fix it? Thank you! 

// Adjust paragraph style to even/odd pages script
// Written for Adobe InDesign

// Function to check if a page is even or odd
function isEvenPage(page) {
  return page.side == PageSideOptions.LEFT_HAND;
}

// Function to change paragraph style based on even/odd page
function adjustParagraphStyles(doc) {
  var pages = doc.pages;
  
  for (var i = 0; i < pages.length; i++) {
    var page = pages[i];
    var pageTextFrames = page.textFrames;
    
    for (var j = 0; j < pageTextFrames.length; j++) {
      var textFrame = pageTextFrames[j];
      var paragraphs = textFrame.paragraphs;
      
      for (var k = 0; k < paragraphs.length; k++) {
        var paragraph = paragraphs[k];
        var styleName = paragraph.appliedParagraphStyle.name;
        
        if (isEvenPage(page)) { // Even page
          if (styleName == "N. Artigo - p.impar") {
            paragraph.appliedParagraphStyle = doc.paragraphStyles.itemByName("N. Artigo - p.par");
          }
        } else { // Odd page
          if (styleName == "N. Artigo - p.par") {
            paragraph.appliedParagraphStyle = doc.paragraphStyles.itemByName("N. Artigo - p.impar");
          }
        }
      }
    }
  }
}

// Main script execution
var doc = app.activeDocument;
app.doScript(adjustParagraphStyles, undefined, undefined, UndoModes.FAST_ENTIRE_SCRIPT, "Adjust paragraph style to even/odd pages");