Pattern Script Not Working in Illustrator

Hello All,

I have been given a Script for Adobe Illustrator but when I run it, nothing appears to occur. The Script is supposed to find colors that have a tint in them and create a dot pattern and apply it onto the color. I run the script and Illustrator thinks for a couple of seconds and then nothing, not even an error. It doesn't appear to be a complex one - any ideas where the problem is?

// Define the size of the dots in millimeters
var dotSize = 1.5;

// Define the patterns for each percentage range
var patterns = [
  {
    min: 10,
    max: 20,
    spacing: 3
  },
  {
    min: 21,
    max: 30,
    spacing: 2.5
  },
  {
    min: 31,
    max: 40,
    spacing: 2
  },
  {
    min: 41,
    max: 50,
    spacing: 1.5
  },
  {
    min: 51,
    max: 60,
    spacing: 1
  },
  {
    min: 61,
    max: 70,
    spacing: 0.5
  },
  {
    min: 71,
    max: 80,
    spacing: 0.25
  }
];

// Get the active document and loop through its swatches
var doc = app.activeDocument;
for (var i = 0; i < doc.swatches.length; i++) {
  var swatch = doc.swatches[i];
  if (swatch.colorType == ColorModel.SPOT && swatch.tint != 100) {
    // Create a new pattern swatch for the current color and tint
    var pattern = doc.swatches.add();
    pattern.colorType = ColorModel.PATTERN;
    pattern.name = swatch.name + " Pattern";
    pattern.pattern = doc.patterns.add();
    pattern.pattern.name = swatch.name + " Pattern";
    pattern.pattern.width = dotSize;
    pattern.pattern.height = dotSize;
    pattern.pattern.spaceBefore = 0;
    pattern.pattern.spaceAfter = 0;
    pattern.pattern.dotSize = dotSize;
    pattern.pattern.angle = 0;
    pattern.pattern.spacing = getSpacing(swatch.tint);
    pattern.pattern.fillColor = swatch.color;
    pattern.pattern.strokeColor = swatch.color;

    // Apply the pattern swatch to all artwork that uses the current swatch
    applyPatternSwatch(swatch, pattern);
  }
}

// Get the spacing for the given tint
function getSpacing(tint) {
  for (var i = 0; i < patterns.length; i++) {
    var pattern = patterns[i];
    if (tint >= pattern.min && tint <= pattern.max) {
      return pattern.spacing;
    }
  }
  // If the tint is over 80%, use solid fill color instead of pattern
  return 0;
}

// Apply the given pattern swatch to all artwork that uses the given swatch
function applyPatternSwatch(swatch, patternSwatch) {
  for (var i = 0; i < doc.pageItems.length; i++) {
    var item = doc.pageItems[i];
    if (item.fillColor && item.fillColor.spot && item.fillColor.spot.name == swatch.name) {
      item.fillColor = patternSwatch.color;
      item.fillColor.pattern = patternSwatch.pattern;
    }
    if (item.strokeColor && item.strokeColor.spot && item.strokeColor.spot.name == swatch.name) {
      item.strokeColor = patternSwatch.color;
      item.strokeColor.pattern = patternSwatch.pattern;
    }
  }
}