Eliminating some notices in FUNCTION value_defined

Hi!
I got php notices like this
Notice: Undefined index: SOME_VAR in E:\Projects\SomeProject\cls_fast_template.php on line 605

I'm not sure that it's a bug, but I fixed it next way:
in FUNCTION value_defined($value, $field = '', $params = '')
changed lines
$var = $this->PARSEVARS [$value];
if ($field {0} == '.') {
to
$var = NULL;
if (array_key_exists($value, $this->PARSEVARS))
{
$var = $this->PARSEVARS [$value];
}
if (strlen($field)>0 && $field {0} == '.') {

I have proposed this to review, thank you.