validation - I didn't set "VALID_NOT_EMPTY" but it become required field

In my model,
============================================
var $validate = array(
'name'=>array(
'no_empty'=>array(
'rule'=>VALID_NOT_EMPTY,
'message'=>'Please enter your name'
)
),
'email'=>array(
'emailchk1'=>array(
'rule'=>VALID_EMAIL,
'message'=>'Please enter valid email address'
)

)

);
============================================

The Name field is required field but email is not but when I don't
fill email,
then I get email error message, 'Please enter valid email address'.

I didn't make email field as required filed but I can not continue
unless I fill in email address.

What's going on??