test.erl:15: variable '_Else' unsafe in 'case' (line 5)

gistfile1.erl

-module(test).
-compile([export_all]).

test() ->
    case true of
        true ->
            ok;
        _Else ->
            ok
    end,

    case true of
        true ->
            ok;
        _Else ->
            ok
    end.

1> c(test).
test.erl:15: variable '_Else' unsafe in 'case' (line 5)
error