[47949591] error shoule be 'can't be blank' if value isn't given

Signed-off-by: Henry Chen <hchen@vmware.com>
fix broken spec of previous commit

Signed-off-by: Henry Chen <hchen@vmware.com>
rollback a unintented commit

Signed-off-by: Henry Chen <hchen@vmware.com>
Merge pull request #109 from Henry-CF/error_format

[47949591] error should be 'can't be blank' if value isn't given