Error: "ns|a" failed to @extend ".foo".
       No selectors matching ".foo" could be unified with "ns|a".
       Use "@extend .foo !optional" if the extend should be able to fail.
        on line 2 of /sass/spec/extend-tests/051_test_element_unification_with_namespaceless_universal_target/input.scss
  Use --trace for backtrace.
