Remove empty line from a multi-line string with Java

I have a multi-line string and some empty lines between other lines. It looks like:

def msg = """
                AAAAAA

                BBBBBB


                CCCCCC

                DDDDDD







                EEEEEE
                TEST
                FFFFF


                GGGGGG
"""

I tried some regex expression with :

msg = msg.replaceAll('(\n\\\\s+\n)+', '')

Or

msg = msg.replaceAll('(\r?\n){2,}', '$1');

But nothing is good about what I'm looking...

Is it possible to remove only empty lines? to get something like that :

def msg = """
                    AAAAAA
                    BBBBBB
                    CCCCCC
                    DDDDDD
                    EEEEEE
                    TEST
                    FFFFF
                    GGGGGG

"""