zendframework/zf2#6496 zendframework/zf2#6386 - minor cleanups, simplifying checks around `$callback` validity
zendframework/zf2#6496 zendframework/zf2#6386 - minor cleanups, simplifying checks around `$callback` validity

zendframework/zend-validator,zf2timo/zend-validator,Maks3w/zend-validator,svycka/zend-validator,weierophinney/zend-validator,akrabat/zend-validator,ezimuel/zend-validator