 
   test "put_bcc/2 should raise if recipient(s) are invalid" do
     assert_raise ArgumentError, fn -> %Email{} |> put_bcc(nil) end
+    assert_raise ArgumentError, fn -> %Email{} |> put_bcc("") end
     assert_raise ArgumentError, fn -> %Email{} |> put_bcc({nil, "bccny@stark.com"}) end
     assert_raise ArgumentError, fn -> %Email{} |> put_bcc([nil, "thor@odinson.com"]) end
     assert_raise ArgumentError, fn ->


  test "to/2 should raise if recipient(s) are invalid" do
    assert_raise ArgumentError, fn -> %Email{} |> to(nil) end
    assert_raise ArgumentError, fn -> %Email{} |> to({nil, "tony@stark.com"}) end
    assert_raise ArgumentError, fn -> %Email{} |> to([nil, "thor@odinson.com"]) end
    assert_raise ArgumentError, fn ->


  test "cc/2 should raise if recipient(s) are invalid" do
    assert_raise ArgumentError, fn -> %Email{} |> cc(nil) end
    assert_raise ArgumentError, fn -> %Email{} |> cc("") end
    assert_raise ArgumentError, fn -> %Email{} |> cc({nil, "ccny@stark.com"}) end
    assert_raise ArgumentError, fn -> %Email{} |> cc([nil, "thor@odinson.com"]) end
    assert_raise ArgumentError, fn ->
