I presume you did this accidentally, and you don't actually want to put a breakpoint on a blank line ...
Not sure what you want here - do you want the DWIM debugger to decide whether you really wanted the breakpoint on a previous non-blank line, or on a subsequent non-blank line?
The debugger doesn't look for a breakpoint and then reads the line; it reads each line and then before executing it checks to see if there is a breakpoint on that line. If the line is empty, it never gets to the point of the breakpoint check.
I did do it accidentally, caught it, and let it go, figuring something reasonable would happen. Later I figured that the debugger never saw the breakpoint and behaved quite reasonably. It's just like a breakpoint on a COMMENT statement (works) versus inside COMMENT/ENDCOMMENT (doesn't work).