JRegistry exists() returns empty array - joomla

Question

I was trying to save a form data to DB. In the controller save() function there is a statement
$data = $model->validate($form, $data);
But it always returns empty. I tracked down the problem to the filter() function in /libraries/joomla/form/form.php (comes with joomla package). Here is some code (shortened):
$input = new JRegistry($data);
$output = new JRegistry;
foreach ($fields as $field)
{
// Initialise variables.
$name = (string) $field['name'];
if ($input->exists($name)){
$output->set($name, $this->filterField($field, $input->get($name, (string) field['default'])));
}
}
$input looks like :
JRegistry Object ( [data:protected] => stdClass Object ( [jform] => stdClass Object ( [title] => Utility Model/Patent application [ap_name] => d ...) [option] => com_eipoapplications [task] => save ) )
And each $name in the loop always contain the form element name (like 'title', 'ap_name' ... ).
But the if conditional statement always returns false. Does any one help me know why JRegistry exists() function is not finding the elements?

Answer 1

I think you are having an inconsistency between form and data.
Let's say the form contains a field with name title.
$data array should have a value under key of same name:
$data = array(
'title' => 'Utility Model/Patent application',
'ap_name' => 'd'
);
Or using print_r
Array
(
[title] => Utility Model/Patent application
[ap_name] => d
)
If there's no data for such field, validation is omitted. If all data keys are wrong, function returns empty array.
The question is, how it happened :/