Using IF-ELSE statement with correlated values

Hi,

I recorded a script with HTML/HTTP protocol for an application developed with JSON script.

In this app, i have 3 dropdowns in which 2 are related and for these i did the correlation. Based on the first dropdown selection, 2nd dropdown values changes.

Here my question is, if 2nd dropdown value is null, it has to select the different value in 1st dropdown. For this, how can i write the code for if-statement.

Thanks in advance for your reply.