Filling in a field only if another field is filled in

[defaultrfjue3aoi30b]

I am looking to have the "AP2_ACCT_NUMBER" field fill in with the number from the "ACCOUNT_NUMBER" field, but ONLY if the "APPLICANT_2_FIRST_SPACE_MIDDLE_SPACE_LAST_SPACE_SUFFIX" is filled out. If that field is blank then I do not want anything to be entered into the "AP2_ACCT_NUMBER" field.

I have tried to research this but I cannot figure it out. I can get it to enter in the same number as the account number field, but then it stays there anytime the "ACCOUNT_NUMBER" field is filled out.

[Nesa Nurani]

As validation script of "APPLICANT_2_FIRST_SPACE_MIDDLE_SPACE_LAST_SPACE_SUFFIX" add this:

this.getField("AP2_ACCT_NUMBER").value = event.value != "" ? this.getField("ACCOUNT_NUMBER").value : "";