Remove `@` before and check for not existing field

[franck-roland]

replace https://github.com/basecrm/basecrm-php/blob/master/lib/Errors/BaseError.php#L18
and do something like
return "resource=" . (isset($error['resource']) ? $error['resource'] : 'no_resource') . " field=" . (isset($error['field']) ? $error['field'] : 'no_field') . " code=" . $error['code'] . " message=" . $error['message'];

All info and warning is an error in my base code and I throw an exception if 'field' does not exist.