Describe your issue
How to fix this error
Hello @dreemincome
Your one or more list indicated in the below image is not populated with any elements. To find out which one it is, perform the steps indicated in below image.
Also have a look on below topic, in case if it helps 
You can’t use local variable, use global, then it will work, I had the same problem 
Have a look at the link @Vaibhav shared, you will find blocks and answers there 