docs: @Override
      public Object getValueAt(Object nodeObj, int column) {
          if (debugger == null) { return null; }
          VariableNode node = (VariableNode)nodeObj;
          switch (column) {
          case 0: // Name
              return node.toString();
          case 1: // Value
              String result;
              try {
                  result = debugger.objectToString(getValue(node));
              } catch (RuntimeException exc) {
                  result = exc.getMessage();
              }
              StringBuilder buf = new StringBuilder();
              int len = result.length();
              for (int i = 0; i < len; i++) {
                  char ch = result.charAt(i);
                  if (Character.isISOControl(ch)) {
                      ch = ' ';
                  }
                  buf.append(ch);
              }
              return buf.toString();
          }
          return null;
      }