Should DEFINE_boolean() allow "None" as the default value?

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Currently, we can define a boolean flag with default value to None:

 FLAGS = gflags.FLAGS
 gflags.DEFINE_boolean("the_flag", None, "The flag.")

I'm not sure if this is expected or should it be allowed, since python-gflags 
project tries to mimic the C++ version of gflags as close as possible.  This is 
troublesome because user may be unaware that a boolean flag can fail both of 
the following assertions:

 assertTrue(FLAGS.the_flag)  # AssertionError: None is not True
 assertFalse(FLAGS.the_flag)  # AssertionError: None is not False

Original issue reported on code.google.com by linshu...@chromium.org on 4 Apr 2012 at 8:04