Pass Non-mandatory Fields Onsubmit Even If Empty (or Tabs Or Blank Spaces)?

I would like to passwith the help of javascript empty non-mandatory fields to my perl script (and replace them with a custom value). The form mailer script only passes the mandatory fields. When non mandatory fields are filled , these are added to the list of passed field values, otherwise the list includes only the mandatory ones. I'd like to pass all values even the empty ones so that the person receiving the submitted data via email can easily export them to a database via a macro written by somebody else. Another requirement from client: The predefined values must not show up in the form fields when loading the page with the form.

How can I check for empty values as well as for tabs or blank spaces and replace each of these fields with a value = "not available"? I tried to do solve this for empty fields (no tabs, no blank spaces) but my solution does not work properly. It requires me to click the submit button 3 times before the form is submitted (because with every click the "not available" value is added in each empty field.

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