Custom fns not being attached to els returned from getListPo

[tonybranfort]

This fails with Failed: clientPo.payments.getRow(...).amount.addTen is not a function:

   // clientPo payments page object
  payments: {
    locator: by.repeater('payment in payments'),
    po: ngpo.makeListPo,
    els: {
      amountInput: {
        locator: by.model('payment.amount'),
        po: ngpo.makeInputPo,
        fns: {
          addTen: function(el, options) {
            return el.getValue()
            .then((val) => {return el.enterValue(Number(val) + 10);});
          }
        }
      },
      amount: {
        locator: by.binding('payment.amount'),
        po: ngpo.makeTextPo},
    },
  },

  // test
    it('should implement custom functions on elements in getListPo', () => {
      expect(clientPo.payments.getRow(0).amount.getValue()).toBe('5'); 
      clientPo.payments.getRow(0).amount.addTen(); 
      expect(clientPo.payments.getRow(0).amount.getValue()).toBe('15'); 
    });