Error in visualising MDPI band

Question

I am trying to stack a 3 band image (2 NDVI bands and 1 MDPI band). There is some error when I am trying to visualise the MDPI band (which is appearing as masked in the Inspector) and hence the stacked image is also not appearing. Where am I going wrong?

var sent2_1=ee.ImageCollection("COPERNICUS/S2")
           .filterBounds(roi)
           .filterDate('2019-11-15','2019-11-17')
           .filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE', 40))
           .mean();

var sent2_2=ee.ImageCollection("COPERNICUS/S2")
           .filterBounds(roi)
           .filterDate('2019-01-10','2019-01-19')
           .filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE', 40))
           .mean();

Map.addLayer(roi); 
print(sent2_2,'sent2');       
Map.addLayer(sent2_2,{min:0,max:3000,bands:['B8','B4','B3']},'sent2');
//Map.centerObject(roi,13);
           
var sent1=ee.ImageCollection('COPERNICUS/S1_GRD')
          .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VV'))
          .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VH'))
          .filter(ee.Filter.eq('instrumentMode', 'IW'))
          .filterDate('2020-03-09','2020-03-10')
          .filterBounds(roi)
          .mean();
 
print(sent1,'sent1');       
Map.addLayer(sent1,{min: [-25, -20, -25], max: [0, 10, 0]},'SAR');

var ndvi=function(image){
  var ndvi_2_2=image.normalizedDifference(['B8', 'B4']).rename('NDVI');
  return image.addBands(ndvi_2_2);
};

var ndvi_1 = ndvi(sent2_1);
print(ndvi_1,'ndvi_1');

var ndvi_2 = ndvi(sent2_2);
print(ndvi_2,'ndvi_2');



var im2 = ndvi_1.select('NDVI');
var im1 = ndvi_2.select('NDVI');

var mpdi_fun=function(image){
  var mpdi=image.normalizedDifference(['VV', 'VH']).rename('MPDI');
  return image.addBands(mpdi);
};

var mpdi = mpdi_fun(sent1);
print(mpdi,'mpdi');

var mpdi_1=mpdi.select('MDPI')
print(mpdi_1,'mpdi_only')
Map.addLayer(mpdi_1,{min:-1, max:1},'MPDI')

var stack=im1.addBands(im2).addBands(mpdi.select('MPDI'));
Map.addLayer(stack,{max:1,min:-1},'stack');
print(stack,'stack');

Answer 1

I think there is a typo in your .select() part:

var mpdi_1=mpdi.select('MPDI') // note how I changed from MPDI to MDPI 

It should be exactly the same as how you wrote it in the .rename() of your mpdi_fun