I am trying to connect my android application to use the Tradeoff Analytics API. Here is part of the code I have used to do this:

     private void showDilemma(final Dilemma dilemma) {
         runOnUiThread(new Runnable() {
             @Override public void run() {
                 tradeoffTextView.setText(dilemma.toString());
             }
         });
     }
 
     private class WatsonTask extends AsyncTask<String, Void, String> {
         @Override
         protected String doInBackground(String... params) {
             showDilemma(tradeoffService.dilemmas(problem).execute());
 
             return "processing tasks done";
         }
 
         @Override
         protected void onPostExecute(String result) {
             tradeoffTextView.setText("Tradeoff Analytics Status: " + result);
         }
 
     }
 
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
         setSupportActionBar(toolbar);
 
         tradeoffButton = (Button) findViewById(R.id.tradeoffButton);
         tradeoffTextView = (TextView) findViewById(R.id.tradeoffTextView);
 
         tradeoffService = initTradeoffAnalytics();
         problem = new Problem("phone");
 
         String price = "price";
         String ram = "ram";
         String screen = "screen";
 
         // Define the objectives
         List<Column> columns = new ArrayList<Column>();
         problem.setColumns(columns);
 
         NumericColumn priceColumn = new NumericColumn();
         **priceColumn.setKey(price);**
         priceColumn.setGoal(Column.Goal.MIN);
         priceColumn.setObjective(true);
         priceColumn.range(0, 400);
         priceColumn.setFullName("Price");
         priceColumn.setFormat("number:2");
         columns.add(priceColumn);
 
         NumericColumn screenColumn = new NumericColumn();
         **priceColumn.setKey(screen);**
         priceColumn.setGoal(Column.Goal.MAX);
         priceColumn.setObjective(true);
         priceColumn.setFullName("Screen");
         priceColumn.setFormat("number:2");
         columns.add(screenColumn);
 
         NumericColumn ramColumn = new NumericColumn();
         **priceColumn.setKey(ram);**
         priceColumn.setGoal(Column.Goal.MAX);
         priceColumn.setFullName("RAM");
         priceColumn.setFormat("number:2");
         columns.add(ramColumn);
 
         // Define the options to choose
         List<Option> options = new ArrayList<Option>();
         problem.setOptions(options);
 
         HashMap<String, Object> galaxySpecs = new HashMap<String, Object>();
         galaxySpecs.put(price, 50);
         galaxySpecs.put(ram, 45);
         galaxySpecs.put(screen, 5);
         options.add(new Option("1", "Galaxy S4").values(galaxySpecs));
 
         HashMap<String, Object> iphoneSpecs = new HashMap<String, Object>();
         iphoneSpecs.put(price, 99);
         iphoneSpecs.put(ram, 40);
         iphoneSpecs.put(screen, 4);
         options.add(new Option("2", "iPhone 5").values(iphoneSpecs));
 
         HashMap<String, Object> optimusSpecs = new HashMap<String, Object>();
         optimusSpecs.put(price, 10);
         optimusSpecs.put(ram, 300);
         optimusSpecs.put(screen, 5);
         options.add(new Option("3", "LG Optimus G").values(optimusSpecs));
 
         tradeoffButton.setOnClickListener(new View.OnClickListener() {
             @Override
             public void onClick(View v) {
                 WatsonTask task = new WatsonTask();
                 task.execute(new String[]{});
 
             }
         });
 }

When I try to execute this code, the application is crashing and I am getting the following error message: E/WatsonService: POST https://gateway.watsonplatform.net/tradeoff-analytics/api/v1/dilemmas, status: 400, error: Data supplied is missing critical information. all objectives must have keys

I am not sure why I am getting this error message seeing as I have checked all the objectives ( price, ram and screen) and they each have a set key. The code is also very similar to that available in the online documentation so I am not sure where I have gone wrong. Any help would be much appreciated, thanks in advance :)