It seems PHP [settype](http://php.net/manual/en/function.settype.php) function doesn't support email type.
Possibles values of type are:
"boolean" (or, since PHP 4.2.0, "bool")
"integer" (or, since PHP 4.2.0, "int")
"float" (only possible since PHP 4.2.0, for older versions use the deprecated variant "double")
"string"
"array"
"object"
"null" (since PHP 4.2.0)
I got error when set a setting's type is "email".
It seems PHP
[settype](http://php.net/manual/en/function.settype.php)
function doesn't supportemail
type.