iterables not working

I am receiving this error when trying to get an array from a graphql query:
"User Error: expected iterable, but did not find one for field RootQuery.blogpostsBetween."
which is odd, since it has worked perfectly fine just a few weeks ago having my Field configured like this:

"blogpostsBetween": &graphql.Field{
Type: graphql.NewList(blogpostType),
Resolve: func(p graphql.ResolveParams) (interface{}, error) {
// ... some more code ...
// what I return here was placed to demonstrate the error.
return [5]Blogpost{}, err
},
Args: graphql.FieldConfigArgument{
"from": &graphql.ArgumentConfig{
Type: graphql.String,
},
"to": &graphql.ArgumentConfig{
Type: graphql.String,
},
},
},

I am really confused on why this is not working anymore, because as I said, I'm quite sure I have not changed anything. But I'd be happy to be wrong.