Unable to create custom transformer for UIFont using AWS style dictionary

I’m using AWS style dictionary to generate UI properties from Figma Tokens. I could not get custom transformer working.

Custom transform and my config file:

import StyleDictionary from "style-dictionary-utils";
import pkg from 'style-dictionary-utils';
const { transform } = pkg;

StyleDictionary.registerTransform({
  name: 'font/createUIFont',
  type: 'value',
  matcher: function(token) {
    return token.attributes.category === 'font';
  },
  transformer: function(token) {
    console.log("hello", token);
    const fontName = token.original.value;
    const fontSize = token.attributes.size.value;

    // Update the transformed value to return UIFont object instantiation
    return `UIFont(name: "${fontName}", size: ${fontSize}) ?? UIFont.systemFont(ofSize: ${fontSize})`;
  }
});

const config = {
  source: ["tokens/**/*tokens.json"],
  platforms: {
    "ios-swift-separate-enums": {
      "transformGroup": "ios-swift-separate",
      "buildPath": "build/ios/",
      "files": [{
          "destination": "FontTokens.swift",
          "format": "ios-swift/class.swift",
          "className": "FontTokens",
          "filter": {
            "attributes": {
              "category": "font"
            }
          },
          "transforms": [
            "font/createUIFont"
          ]
        }]
    }
  },
};

StyleDictionary
  .extend(config)
  .buildAllPlatforms();

the font token:

{
  "font": {
    "headingg": { "$size": 20, "$value": "HelveticaNeue-Bold", "$weight": "bold" }
  }
}

the output I get is:

public class FontTokens {
   public static let headingg = "HelveticaNeue-Bold"
}

What I’m trying to achieve is to create a UIFont property

public class FontTokens {
   public static let headingg = UIFont(name: "HelveticaNeue-Bold", size: 20)
}