By default, all text fields are required. This behaviour is determined by the script but you can make all fields optional by doing the following:

  1. The form should be selected.
  2. Click Form on the left side
  3. Go to the Tools menu and select Custom Script Assistant.
  4. Make sure Object Events is selected
  5. In the Contents box you should see this code: onsubmit="return weCheckForm(this)"
  6. This needs to be deleted or replaced with: onsubmit="return true"

This will allow any fields to be empty and the form still submitted.