Crashes when calling a non existing domain name

[julienmarie]

GenServer.call MrRoboto.Warden, {:crawl?, {"mybot", "http://qweqwq.sdfdsdf.com"}}
** (exit) exited in: GenServer.call(MrRoboto.Warden, {:crawl?, {"mybot", "http://qweqwq.sdfdsdf.com"}}, 5000)
    ** (EXIT) an exception was raised:
        ** (UndefinedFunctionError) function nil.__struct__/0 is undefined or private
            nil.__struct__()
            (elixir) lib/kernel.ex:1672: Kernel.struct/3
            (mr_roboto) lib/mr_roboto/warden.ex:29: MrRoboto.Warden.handle_call/3
            (stdlib) gen_server.erl:615: :gen_server.try_handle_call/4
            (stdlib) gen_server.erl:647: :gen_server.handle_msg/5
            (stdlib) proc_lib.erl:247: :proc_lib.init_p_do_apply/3
    (elixir) lib/gen_server.ex:604: GenServer.call/3
iex(1)> [error] GenServer MrRoboto.Warden terminating
** (UndefinedFunctionError) function nil.__struct__/0 is undefined (module nil is not available)
    nil.__struct__()
    (elixir) lib/kernel.ex:1672: Kernel.struct/3
    (mr_roboto) lib/mr_roboto/warden.ex:29: MrRoboto.Warden.handle_call/3
    (stdlib) gen_server.erl:615: :gen_server.try_handle_call/4
    (stdlib) gen_server.erl:647: :gen_server.handle_msg/5
    (stdlib) proc_lib.erl:247: :proc_lib.init_p_do_apply/3
Last message: {:crawl?, {"mybot", "http://qweqwq.sdfdsdf.com"}}
State: %{}