view mercurial/__init__.py @ 25448:2bbfc2042d93

dirstate: avoid invalidating every entries when list is empty

Default value was not tested with 'is None', this made empty list seen as
default value and result the invalidation of every single entry in the
dirstate. On repos with hundred of thousand of files, this results in minutes
of lookup time instead nothing.

This is a text book example of why we should test 'is None' if this is what we
mean.