[WIP] allow empty string in enum set methods

[mgyucht]

Changes

WIP PR with the idea to support empty string in Set() methods for enums. This allows simpler setting of optional enum values, bypassing validation for optional fields in other structures.

Tests

• make test passing
• make fmt applied
• relevant integration tests applied

[nfx]

why do we want to allow this?..

@hong-db was putting out a proposal for UNSPECIFIED enum value for "empty" values

[mgyucht]

Yeah, I marked it WIP because I'm not sure whether we actually want this or not.

The idea is that optional enum fields are represented as empty strings in structures. When you know the value you want to set an enum field to, you can simply assign it. However, you can't just say req.EnumField.Set(x) without checking if x is empty. However, an enum may be optional in some contexts and required in others, because optional or not is not a type-level decision, it is a field-level one. So here I propose adding it just in the Set() method for all enums to support optional enum fields, basically that a user can use empty string in the Set() method to indicate that the field shouldn't be sent in the request without introducing an empty string enum value (which we definitely don't want).

[nfx]

empty string for enum feels wrong 🤷 it might not work in other languages consistently

[mgyucht]

Python has None and Java has null, it's just Go with this problem I think. It's not that we're adding an enum value of empty string, but since Go doesn't have enums, and this is also the behavior or omitempty, it seems like it could be OK to do this