Invalid properties validation

An issue was raised on tdc side, last s3 component change does not work on dataset:
https://jira.talendforge.org/browse/TDC-4820

S3 connection properties now hold a new enumeration, signingRegion.
This enum is not tagged as required, and has a default value.
The expected behavior would be to have old properties, with no signingRegion defined, still be valid.

However, it looks like enum are considered as required despite not being tagged as such, hence validation fails.

Validation rely on ValidationService, that use JsonSchemaConverter to deduce validation schema.

example :
Calling http://dataset:80/tacokit-proxy/v1/configurations/persistence/save/datastore

payload:

{"configuration":

{"accessKey":"AKIAQZPJGO2AYWOHDXWB","secretKey":"...","specifyCredentials":true}

,"$formId":"ZmlsZWlvI0ZpbGVJTyNkYXRhc3RvcmUjUzNEYXRhU3RvcmU","$remoteEngineId":"cf1fca8e-54fe-4dfd-a633-1d16075d897d","$connectionMetadata":{"name":"S3Datastore - Wed Oct 14 10:11:53 AM CEST 2020","type":"ZmlsZWlvI0ZpbGVJTyNkYXRhc3RvcmUjUzNEYXRhU3RvcmU","remoteEngine":"cf1fca8e-54fe-4dfd-a633-1d16075d897d"}}

response:

{"timestamp":1602663111178,"status":500,"error":"Internal server error","message":"ValidationService.ValidationError(field=/configuration/signingRegion, message=Invalid value, got null, expected: [\"DEFAULT\",\"AP_SOUTH_1\",\"AP_SOUTHEAST_1\",\"AP_SOUTHEAST_2\",\"AP_NORTHEAST_1\",\"AP_NORTHEAST_2\",\"CN_NORTH_1\",\"CN_NORTHWEST_1\",\"EU_WEST_1\",\"EU_WEST_2\",\"EU_WEST_3\",\"EU_CENTRAL_1\",\"GovCloud\",\"CA_CENTRAL_1\",\"SA_EAST_1\",\"US_EAST_1\",\"US_EAST_2\",\"US_WEST_1\",\"US_WEST_2\"])","path":"/tacokit-proxy/v1/configurations/persistence/save/datastore"}