Webform multistep form (wizard) calculated field empty

Oh, forgot to mention fields num1 and num2 are optional.

Hi @igorbiki thanks for reporting the issue.
I could reproduce the issue.
I added the unit test for the issue and also i'm adding the patch to fix it.

This fixes optional fields vs required ones.

Even with the patch, if both input fields are on wizard's first page, and calculation field (sum) is on the second, the sum is empty.

This is how webform looks like:
- page 1
+ number field, first
+ number field, second
- page 2
+ calculation field, sum with ":first|0 + :second|0"

Here is webform export as well, hope it helps.

Thanks @igorbiki for the quick update.
I could reproduce the issue. I'll take a look.