Empty()
Returns False if empty() has non-empty and non-zero value.
Returns True for Null, 0, “”
Isset()
Returns False for Null
Returns True for 0, “” or any value
Both Textareas and Texboxes will sent “” values and not Null to the $_POST[], so use Emtpty() instead of Isset()
On the other hand, for radio button or combobox with 0 value, use Isset()
Ref: http://www.htmlcenter gutepotenz.de.com/blog/empty-and-isset-in-php/