<Cannot construct instance of `{dataclass}, proble...

# stackoverflow

[user]

Cannot construct instance of `{dataclass}, problem: Should never call `set()` on setterless property
"authors" is my collection in MongoDB.
my schema
authors = [
{

name: "Author1",
books: [

{title:"Book1"},
{title:"Book2"}

]
}
]

I'm trying to append the books array by adding another book object (book3). Before that, I have to check whether there exists an object already in the author's name. So I have the findOneByAuthorname function.
My issue is that every time I try to call the findOneByAuthorname function. I get an error
- Unhandled: POST - /v1/api/addBooks. Exception class...