Function.Returns<> non primitive type error

Microsoft.AspNetCore.OData v8.0.8

In my EDM model I have a function declared in this way:

function = builder.Function("MyFunction");
function.Parameter<int>("customId");
function.Returns<MyTypedClass>();

If I call the function, the server response will be:

{

If I change the Returns to ReturnsCollection:

function = builder.Function("MyFunction");
function.Parameter<int>("customId");
function.ReturnsCollection<MyTypedClass>();

works correctly, but I need to return an array of 1 element. It's not necessary.