Generate a CSS ruleset for every layer of the current page of a Sketch document

Generate Stylesheet.sketchplugin

var allLayers = sketch.doc.currentPage().layers();

function createRuleSetStr (layer) {
  var str = '';
  var selector = '.' + layer.name().toLowerCase().replace(/ /gi, '-');
  var attrs = layer.CSSAttributes();

  str += selector + ' {';

  for (var i = 0; i < attrs.count(); i += 1) {
    var declaration = attrs.objectAtIndex(i);

    // Sketch adds a comment to each rule set that is the name of the layer.
    // Don't include that.
    if (declaration.indexOf('/*') < 0) {
      str += '\n\t' + declaration;
    }
  }

  str += '\n}';

  return str;
}

function generateStyleSheet () {
  var stylesheet = '';

  for (var i = 0; i < allLayers.count(); i += 1) {
    var layer = allLayers.objectAtIndex(i);
    stylesheet += '\n\n' + createRuleSetStr(layer);
  }

  return stylesheet;
}

var styleSheetString = generateStyleSheet();

log(styleSheetString);

Ok I figured out what was going on with my Sketch file. You can't have artboards and you can't have groups. Once I removed both of those it worked.