You can add Logic with negative conditions to blank fields, but you cannot use positive conditions.
Positive conditions, like is equal to, begins with, ends with, and contains won't work with an empty value.
In the scenario below, I want to jump to question #4 as long as the respondent doesn't leave question #1 empty, and I want to set up my conditions accordingly.
In the screenshot below, a logical rule with the is equal to condition and a blank field is used. This might seem like a rational approach, but Logic doesn’t work this way.
You'll also see an error message explaining the issue, and a warning will appear in your Logic Map:
What you can do instead is use negative conditions and “reverse logic”. Add the is not equal to condition to the blank field, and the question you want users to jump to when they don’t leave the answer field empty.
Below is an example of the method that will work seamlessly with Logic:
Additionally, you can only use this solution if you also set a value for In ALL other cases jump to, so that Logic knows where to direct respondents who leave the question empty.