Patch from Perry Stoll: OK for list of modules to be empty.
diff --git a/Lib/distutils/command/build_py.py b/Lib/distutils/command/build_py.py
index d956eef..d75bf3f 100644
--- a/Lib/distutils/command/build_py.py
+++ b/Lib/distutils/command/build_py.py
@@ -55,6 +55,10 @@
# input and output filenames and checking for missing
# input files.
+ # it's ok not to have *any* py files, right?
+ if not modules:
+ return
+
# XXX we should allow for wildcards, so eg. the Distutils setup.py
# file would just have to say
# py_modules = ['distutils.*', 'distutils.command.*']