D-Programming-Language/phobos — pull request #632 by 9rnsr (2012-06-15 03:47:26+00:00)
Title: Issue 8240 - std.algorithm.joiner and empty inputRangeObject

http://d.puremagic.com/issues/show_bug.cgi?id=8240

In this case, _current member is invalid at the start of iteration.
Then, `if _items.front` is not an lvalue, joiner should have additional member
`_valid_current`.