Working on LULC classification by Random Forest Algo. Getting an error when I want to add the chart layer of classified image

Question

I am working on the LULC classification by Random Forest Algorithm using GOOGLE EARTH ENGINE(GEE). I have classified the satellite image into four classes- water, vegetation, bareland and builtup. I want to print the chart of the classified image which will give the graph representation of the classified image.

I have tried the code below:

// Create a chart of classified image
var chart = ui.Chart.image.histogram({
  image: classified,
  region: roi,
  scale: 30,
  minBucketWidth: 10
}).setOptions({
  title: 'Class Histogram'
});

// Add the chart to the map
Map.add(chart);

And getting an error: