query execution error when using @interfaceObject

[maxrad82]

Issue Description

I'm experiencing a very strange behaviour using the @interfaceObject directive

Considering 3 services

Service 1:

        extend schema
        @link(url: "https://specs.apollo.dev/federation/v2.3",
            import: ["@key"])

        interface Product @key(fields:"id") {
            id: ID!
        }

        type Book implements Product @key(fields:"id") {
            id:ID!
            title: String
        }

        type Query {
            allProducts: [Product!]!
        }

Service 2:

        extend schema
        @link(url: "https://specs.apollo.dev/federation/v2.3",
            import: ["@key", "@interfaceObject"])

        type Product @key(fields:"id") @interfaceObject {
            id: ID!
            reviews: [String!]!
        }

Service 3:

        extend schema
        @link(url: "https://specs.apollo.dev/federation/v2.3",
            import: ["@key", "@interfaceObject"])

        type Product @key(fields:"id") @interfaceObject {
            id: ID!
        }

        type Query {
            searchProducts: [Product!]!
        }

depending on the query, it may failed, suceed or be inconsistant

  searchProducts {
    id
    reviews    
  }

=> ok

  searchProducts {
    __typename
    id
    reviews    
  } 

=> error "Cannot return null for non-nullable array element of type Product at index 0"

  searchProducts {
    id
    ...on Book {
      reviews
    }    
  }

=> inconsistant result, missing reviews field

I have linked a github repo to reproduce this issue. I'm pretty sure the implementation is correct according the documentation

Link to Reproduction

https://github.com/maxrad82/apollo-federation-bug-interface

Reproduction Steps

Prerequisite:

• docker
• docker-compose
• rover

clone the repository and run make run to start the subgraphs and the supergraph
go to http://localhost:4007

run the followng queries:

query ExampleQuery {  
  searchProducts {
    id
    reviews
  }
}

=> ok

query ExampleQuery {  
  searchProducts {
   __typename
    id
    reviews
  }
}

=> fails

query ExampleQuery {  
  searchProducts {
    id
    ...on Book {
      reviews
    }    
  }
}

=> reviews is not return