Fix element value check

[dariuszz123]

Empty data check for form value should be done by comparing it to null.
Current implementation with empty() check is wrong, because values like "0" are false positive.
For example:

$value = "0";
empty($value); #return true witch obviously is incorrect
(null === $value); #return false witch is correct

[ndenoncourt]

May I ask why you closed this?

[dariuszz123]

Replaced with new PR #14