Problem with Lambda mutation

[JatinDevDG (Jatin Dev)]

Hi @SamSamit , i am not able to reproduce the error that you specified on addUser mutation.
Which version of Dgraph are you using ?
I tried it on master branch and our previous releases 20.11 and 20.07, and it works perfectly fine for me.
i used some part of your schema

type User @secret(field: "password") {
  username: String! @id
  email: String!
  characters: [Character] @hasInverse(field: owner)
  role: UserRole! @search
}

enum UserRole {
  USER
  ADMIN
}

type Character
  @auth(
    query: {
      rule: """
      query ($USER: String!) {
          queryCharacter{
              owner(filter:{username: { eq: $USER }}){
                username
              }
          }
      }
      """
    }
  ) {
  id: ID!
  name: String!
  race: String!
  owner: User! @hasInverse(field: characters)
}

And ran below mutation with variable, it works fine.