--- rect-orig.el	2023-01-31 17:25:08.498658466 +0300
+++ rect-patched.el	2023-02-02 20:21:11.041198925 +0300
@@ -144,11 +144,18 @@
 
 ;;; Rectangle operations.
 
+(defvar rectangle-select-skip-line nil
+  "Control the `apply-on-rectangle' execution.
+`nil' -- apply action to selected lines, `t' -- skip empty lines,
+`function' -- skip line if it return non-`nil'.
+The function get all arguments of `apply-on-rectangle' as input.")
+
 (defun apply-on-rectangle (function start end &rest args)
   "Call FUNCTION for each line of rectangle with corners at START, END.
 FUNCTION is called with two arguments: the start and end columns of the
 rectangle, plus ARGS extra arguments.  Point is at the beginning of line when
 the function is called.
+The `rectangle-select-skip-line' variable allow to skip lines.
 The final point after the last operation will be returned."
   (save-excursion
     (let* ((cols (rectangle--pos-cols start end))
@@ -166,7 +173,14 @@
       (goto-char startpt)
       (while
           (progn
-            (apply function startcol endcol args)
+            (when (cond
+                   ((null rectangle-select-skip-line)
+                    t)
+                   ((functionp rectangle-select-skip-line)
+                    (apply rectangle-select-skip-line function start end args))
+                   (t
+                    (not (string-match-p "\\`\\s-*$" (thing-at-point 'line)))))
+              (apply function startcol endcol args))
             (setq final-point (point))
             (and (zerop (forward-line 1)) (bolp)
                  (<= (point) endpt))))