Matching blank lines with regular expressions

I've got a string that I'm trying to split into chunks based on blank lines.

Given a string s, I thought I could do this:

re.split('(?m)^\s*$', s)

This works in some cases:

>>> s = 'foo\nbar\n \nbaz'
>>> re.split('(?m)^\s*$', s)
['foo\nbar\n', '\nbaz']

But it doesn't work if the line is completely empty:

>>> s = 'foo\nbar\n\nbaz'
>>> re.split('(?m)^\s*$', s)
['foo\nbar\n\nbaz']

What am I doing wrong?

[python 2.5; no difference if I compile '^\s*$' with re.MULTILINE and use the compiled expression instead]