terminates and provides back **None**.

This blanks any content within the space that the input field is rendered
(otherwise stray characters would be interpreted as part of the initial
input).

:param int x: horizontal location
:param int y: vertical location
:param str initial_text: initial input of the field
:param list backlog: previous inputs that can be selected by pressing
  up/down, oldest to newest
:param func tab_completion: function to suggest inputs to tab complete with

:returns: **str** with the user input or **None** if the prompt is canceled
Nr+