fix #193: Connector deserialization when tariffIds is absent from json

[lilgallon]

closes #193

Updated SkipNullsListSerializer.deserialize to follow the standard kotlinx.serialization convention for nullable serializers: check decoder.decodeNotNullMark() before reading any token from the stream. When the decoder signals the value is null (either because the field is absent or because the JSON value is null), the method now returns null immediately without touching the stream.

  // Before
  return when (val jsonElement = jsonDecoder.decodeJsonElement()) {
      is JsonNull -> null
      is JsonArray -> { ... }
      else -> throw SerializationException("Expected array or null for List")
  }

  // After
  if (!decoder.decodeNotNullMark()) return decoder.decodeNull()
  return when (val jsonElement = jsonDecoder.decodeJsonElement()) {
      is JsonArray -> { ... }
      else -> throw SerializationException("Expected array for List")
  }

Added two new parameterized test cases in ConnectorMapperTest (run against all available serializers):

• tariff_ids field entirely absent from JSON → tariffIds decoded as null
• "tariff_ids": null explicit null in JSON → tariffIds decoded as null

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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