landsat - Writing code for monthly NDVI medians in Google Earth Engine?

My goal is to get monthly NDVI medians in Google Earth Engine. This helpful post got me started: reduce image collection to get annual monthly sum precipitation

However, I am using Landsat (not MODIS). This script does run but the map layer has "no bands to visualize".

1. How can I visualize the bands? (Maybe the issue is that this dataset only has 1 band?).


2. How can I add all 12 map layers, one per month? (perhaps with stacking?)

var ndvi = ee.ImageCollection('LANDSAT/LT5_L1T_32DAY_NDVI');

var months = ee.List.sequence(1, 12);


// Group by month, and then reduce within groups by mean();
// the result is an ImageCollection with one image for each
// month.
var byMonth = ee.ImageCollection.fromImages(
  months.map(function (m) {
    return ndvi.filter(ee.Filter.calendarRange(m, m, 'month'))
                .select().median()
                .set('month', m);
}));
print(byMonth);


Map.addLayer(ee.Image(byMonth.first()));