ZF-5764: Zend_Form should note that '0' value is valid since 1.7 even with required=>true and notEmpty validator
Since 1.7 (I think) when creating form element and setting value 0 it will pass the notEmpty and required=>true validator. 0 is now considered valid value. Now one should enter empty string instead. I am not 100% if this is all 1.7 issue but on 1.6.2 '0' was not valid with above validators.