If you set it in code, why do you need the mandatory flag set?

Does setting the mandatory flag to false fix the problem?

Even I have faced a similar issue, it just does not come into the code. Setting the mandatory flag to false does fix the problem but the requirement is to have it mandatory.

This happens when i create a page with the property not set to mandatory (and dont enter any content in it) and later on if we modify the property as mandatory, you get this error since the page is already created. These errors are generally done by admin users who are not aware of these kind of implications, well i want to build my code in such a way that the errors made by illiterate users are caught and handled ie, make my code more robust. Is there any way to catch these types of exceptions as it takes the whole site down rather than just the created page.