How to do error handling for GraphQL server using FSharp.Data.GraphQL in F#? - f#

Question

I am using FSharp.Data.GraphQL for implementing GraphQL server. The documentation is not very clear about error handling. In the following mutation resolver, I wish to return errors if user provides invalid values for email and password:
let login =
Define.AsyncField(
name = "login",
typedef = Nullable Output.Token,
description = "Login using email and password",
args = [
Define.Input("email", String)
Define.Input("password", String)
],
resolve =
fun ctx _ ->
// ... some more code related to db and validation
let customErr: exn = Error.InvalidUserPassword
// This statement has not effect
ctx.AddError customErr
// Should I use raise to explicitly throw exception
// raise customErr
Async.result None
)
Looking into the source code, I found out AddError method on ResolveFieldContext. But it seems to produce no effect on the final result of the mutation. The output is always without any error:
{
"documentId": 1234,
"data": {
"login": null
},
// The errors array is not available
"errors": []
}
Should I raise the exception to add the error handling? And, if that is the case, how can I go about adding multiple error codes as part of single query or mutation since I can raise only one exception?