How do I check if a given variable is empty?

1. How do I check if a given variable is empty?

During data Processing, Google Analytics:

16. During data Processing, Google Analytics:

Which of the following are required in order to see data for each page of a three-page conversion process in the Goal Flow report?

17. Which of the following are required in order to see data for each page of a three-page conversion process in the Goal Flow report?