When you bind to a form element in the insert behavior, the code entered by default is sort of shortened if statement called a ternary expression.
the code will look similar to:
<?php echo((isset($_POST["realvacdate"]))?$_POST["realvacdate"]:"") ?>
The long form using an if statement for this would be:
<?php
if(isset($_POST["realvacdate"])) {
echo($_POST["realvacdate"]);
} else {
echo("");
}
?>
you could modify the ternary expression to also check for a blank value:
<?php echo((isset($_POST["realvacdate"]) || $_POST["realvacdate"] != "")?$_POST["realvacdate"]:"") ?>
you can also further modify this expression to use something besides a blank string if it is false:
<?php echo((isset($_POST["realvacdate"]) || $_POST["realvacdate"] != "")?$_POST["realvacdate"]:"This is my false value") ?>