[O] c-c ' strips final newline or adds blank line, but never neither

[Samuel Wales]

i find that when i do c-c ' on a source block, it either strips the
final newline in the editing buffer or adds an unwanted blank line in
the source block.

i like to have final newlines in all of my buffers, including editing
buffers.  what setting allows this without introducing a blank line at
the end of a source block?

thanks.