.getText() (note there’s nothing inside the brackets) should get the innerHTML property, but if your element doesn’t have any innerHTML, but instead has text written (e.g. it is an input element), .getAttribute('value') should get you what you need.
Anyway, this is just some guesswork, if I didn’t hit anything, follow the advice given here:
From the behavior you describe I suspect that the span actually doesn’t contain any text. Can you provide a screenshot of the HTML page ? You can obtain it by right click on the span -> Inspect.