title: property 'pc2' of feature '1_1_1_1_0_0' is missing
body: <p>while using google earth engine to classify the land use of an area, the error of property 'pc2' of feature '1_1_1_1_0_0' is missing, appears.
  actually this error appears for all bands of my testing data. here is my code:</p>
  
  <pre><code>var classesT = t_forest_2001.merge(t_rice_2001).merge(t_dryfarm_2001).merge(t_village_2001)
    .merge(t_water_2001) .merge(t_bare_2001);
    print(classesT);
    Map.addLayer(classesT ,{}, 'test');
    var bands = ['PC2','PC1','slope', 'NDWI','NDVI','NDBI','texture'];
   var testing = classified.sampleRegions({
                                         collection: classesT,
                                         properties:['landuse'],
                                         scale: 30
                                                        });
  
  //var con=  testing.errorMatrix('landuse','classification')
  //print ('accu',con.producersAccuracy().project([0]));                                                    
    //var classifiedT = testing.select(bands).classify(classifier);
    Map.addLayer(classified ,{min:0, max:5, palette: ['#358521', '#63ff60',
    '#ffb783', '#be3939','#68f8ff','#ffe78f']},'classification');
  
   var confusionMatrix = ee.ConfusionMatrix(testing.classify(classifier)
                       .errorMatrix({
                         actual: 'landuse', 
                         predicted: 'classification'
                                       }));
  print('Test:', confusionMatrix);
  print('Overall Accuracy Test:', confusionMatrix.accuracy());
  print('kappa Test:', confusionMatrix.kappa());
  print('Producers Accuracy Test:', confusionMatrix.producersAccuracy());
  print('Consumers Accuracy Test:', confusionMatrix.consumersAccuracy());
  </code></pre>