FIX: 'click_on()' method

[lf2a]

@only_if_element raises an error because self.state.element is None. self.click(x, y) doesn't have x, y params.

@only_if_element
def click_on(self, label):
    """
    Click on the element.

    Args:
        label (str): The image identifier
    """
    x, y = self.get_element_coords_centered(label)
    self.click(x, y)