Bug: Impossible to clear numeric value

```
TextField amountField = new TextField("Amount:");
ResetButtonForTextField.extend(amountField);
InputMask amountInputMask = new InputMask(Alias.CURRENCY);
amountInputMask.setClearMaskOnLostFocus(true);
```
Will show empty "Amount:" field till you type something. When you clear the value field remain "$ 0.00" forever (and is no way to clear the value and set it to null/"").