Optional-defined fields with validation rules are saved in the storage and can violate Response Validation

[oxisto]

Discussed in #1010

^{Originally posted by lebogg March 14, 2023}
Even when we use optional for a proto field (see example below), the storage will save the respective tuple with a zero value of this field (e.g. empty string in the raw field). When we then call ListEvidences, e.g., we (in theory) can have a validation error since we have filled the field raw with empty string but now validation rules apply (min length 1 in this example). Thus, we would get errors when we check these evidences with corresponding validation methods. e.g. with the validation on the response (func (m *ListEvidencesResponse) Validate()). This currently happens in the new tests of #999, where we use the response validation method.

The question is: Do we just ignore it; adjust the .proto files; or adjust storage operations to make nil entries if that is even possible.

Example:

clouditor/api/evidence/evidence.proto

Line 57 in a718fcf

optional string raw = 5 [ (validate.rules).string.min_len = 1 ];

This seems strange because the database can handle NULL fields, so sin this case null/nil should be stored in the DB instead of "". Maybe we need to set a different "default value" (see https://gorm.io/docs/models.html#Fields-Tags, tag default).

[oxisto]

We should check, whether nullable/optional fields are really stored as "null" in the database (and not as an empty string for example)