Empty embedded structs support

[vheathen]

Hi!

Thanks for the project, it is very useful.

I would kindly ask about a decision behind the empty maps handling.

Currently, on cast it sees an empty map as a nil value. But in my case it is possible to have embedded empty structs, because the name (module) of the struct is a value by itself.

I also use :use_parent_field_for_type parameter to get the structure type. Everything works until I try to read a record with an empty struct (and it is clear why: nothing is written to the DB if parameters map is empty) and if I add the __type__ field into a params map - I get ** (CondClauseError) no cond clause evaluated to a truthy value as per one the issues.

So, I'm trying to understand how to solve the problem other than adding fake data into the empty structures.

Thank you!

[dimakula]

I encountered the same issue, and have a fix for it here: #139

From what I can tell, there's no good reason for treating an empty map as a nil here: if : use_parent_field_for_type is set, then we can infer the type of the empty map from the parent type. And if the type cannot be inferred from either the parent or the embedded map, then we should defer to the :on_type_not_found option to do the right thing in the case of an empty map, instead of just treating it as a nil. But I'll defer to the project's maintainer for guidance on this matter 🙏