Getting text from next non-blank line

[Heime]

This interactive function requests the user to input a string associated with 
the current line number.  I want to change it so that the function picks out
the text on the current line or the text of the next non-blank line.  But also
allow the user to write their own text for the line.

(defun tema-mark (kfrz)
  "Associate line number at cursor position with key phrase KFRZ."
  (interactive "sString: ")

  (let ( (lnum (line-number-at-pos)) )

    (setq-local tema-lugar
                 (append tema-lugar (list (cons kfrz lnum)))) ))