ASN: Optional field not used

Several of the fields of the data structure are optional and you have an Optional column. But the optionality seems to be ignored at the moment

The problem is that if the field is not set, you will generate an invalid ASN.1 string:

Just to be clear:

• if the OPTIONAL attribute is set in the grammar, and the user did not fill any value, then the field should be ignored when serializing the value (here, gateway and dns should not appear at all in the serialized string saved in the model)
• if the DEFAULT attribute is set (e.g. for the "version" field) and the value is not changed from the default, the field may also be omitted from the serialized string.

ip.asn