This filter removes blank lines using the DECTPU
  keywords LINE_BEGIN and LINE_END.

     global_replace( LINE_BEGIN + LINE_END, '');

  The LINE_END keyword absorbs the new line.

  The above filter only replaces lines containing no
  characters. The following filter also replaces lines
  containing only spaces and tab characters:

     global_replace( LINE_BEGIN + (white_space|null) +
         LINE_END, '');