[zendframework/zf2#1693] Add null case to conditional
[zendframework/zf2#1693] Add null case to conditional

- Check for empty name was modified to check for only empty string,
  causing a regression; it needed to also check for null

adamlundrigan/zend-form,zendframework/zend-form,svycka/zend-form,svycka/zend-form,marek-saji/zend-form,zendframework/zend-form,akrabat/zend-form,MadCat34/zend-form,MadCat34/zend-form,akrabat/zend-form,adamlundrigan/zend-form,marek-saji/zend-form