Remove unused/mutable default args

Having mutable default args is a bad idea
(http://docs.python-guide.org/en/latest/writing/gotchas/#mutable-default-arguments).

The places where a new object would not be instantiated were left alone,
since it wouldn't make any difference (the same object would be
referenced anyway).

Change-Id: If71154d9bdb42f3ee284c4478c3ee7b177ec8009
Merge "Remove unused/mutable default args"