Error While Creating a structure

Hi Expert,

I am facing any issue when trying to create a structure. When i tried to associate items getting any error. " Failure- java.lang.NumberFormatException:null"

Below are the steps which i have followed for creating the structure.

1)Launch Procut workbench
2) Seach an item(Item a)
3) right clik on the item(Item a)
4) click on create the structure
5) right click on the item(Item a)
6) click on add
7) search for item(Item b) that we want to associate under it
8) click on save

When i tried to associate Item a with item b, I am getting any error.

The below error is fixed after making the below changes