- avoid uninitialized value warnings like the following:
    Use of uninitialized value $target_base in ...
- example of Cwd::realpath can returning undef:
  $ perl -wl -MCwd -e 'my $p=Cwd::realpath(shift); print "p($p)";' "/path/has a/space"
  Use of uninitialized value $p in concatenation (.) or string at -e line 1.
  p()
Merge branch 'dfm-uninitialized-warnings'