I assume that you have a form that requires some information to be entered for the form to proceed, and let's spouse that you do check if required fields are empty or not using JavaScript or any other Client-Side scripting technology.

Problem # 1

with Client-Side scripting language the user's browser must support that language for your script to run, so if user doesn't have a JavaScript enabled (for example) browser your script will not work, this will allow users easily to submit the form without those required fields, causing errors that

1. give false impression that your web is not working
2. those errors can be useful for hackers especially when they contains physical locations like C:\folder\file.asp

Problem # 2

Some people can also play around your code they can make there own forms pointing at your submission page, so they can get errors

Solution

To prevent users from getting these errors you can make the page which actually submit the form checks if those required fields are empty or not first before submitting them, and you will also add some values (like N/A) to non-Required fields, this make sense cause even if guys try playing around your form they have to submit that form at last to your submission page, Otherwise they will not make problems.

Examples

Our Examples are in ASP, but you can use the concept with any other language

For Required Fields
strName = Request.Form("Name")
If strName = "" Then
response.write "Please enter your Name then try again."
End If

For non-Required Fields
strPhone = Request.Form("Phone")
If strPhone = "" Then
strPhone = "N/A"
End If

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