@cascade directive not properly propagated on Query

Users GraphQL
1

Using the @cascade directive on query directly against dgraph’s GrapgQL endpoint works fine and prunes the results:

query {
  queryAnime(first: 10) @cascade {
    id
    names  {
      localization (filter:{
        id: {eq:"UNDEFINED"}
      }){
        id
      }
      text (filter: {string: {alloftext:"秦时明月 特别篇: 空山鸟语"}}){
        string
      }
    }
  }
}

=>

{
  "data": {
    "queryAnime": [
      {
        "id": "XL84UE",
        "names": [
          {
            "localization": {
              "id": "UNDEFINED"
            },
            "text": {
              "string": "秦时明月 特别篇: 空山鸟语"
            }
          }
        ]
      }
    ]
  },
  "extensions": {
    "touched_uids": 247,
    "tracing": {
      "version": 1,
      "startTime": "2020-08-11T13:33:11.405041351Z",
      "endTime": "2020-08-11T13:33:11.628524341Z",
      "duration": 223483047,
      "execution": {
        "resolvers": [
          {
            "path": [
              "queryAnime"
            ],
            "parentType": "Query",
            "fieldName": "queryAnime",
            "returnType": "[Anime]",
            "startOffset": 135443,
            "duration": 223312664,
            "dgraph": [
              {
                "label": "query",
                "startOffset": 204417,
                "duration": 222921243
              }
            ]
          }
        ]
      }
    }
  }
}

but once dgraph is wrapped by an Apollo Server (using this guide), the directives stops to works:

{
  "data": {
    "queryAnime": [
      {
        "id": "XL84UE",
        "names": [
          null,
          null,
          null,
          null,
          {
            "localization": {
              "id": "UNDEFINED"
            },
            "text": {
              "string": "秦时明月 特别篇: 空山鸟语"
            }
          },
          null
        ]
      },
      {
        "id": "UJKQZ3",
        "names": [
          null,
          null,
          null,
          null,
          null,
          null
        ]
      },
      {
        "id": "M3O5HL",
        "names": [
          null,
          null,
          null,
          null,
          null,
          null
        ]
      },
      {
        "id": "ZC1XA1",
        "names": [
          null,
          null,
          null,
          null,
          null,
          null
        ]
      },
      {
        "id": "K4P8OG",
        "names": [
          null,
          null,
          null,
          null,
          null,
          null
        ]
      },
      {
        "id": "ISJJ6K",
        "names": [
          null,
          null,
          null,
          null,
          null,
          null
        ]
      },
      {
        "id": "0467PM",
        "names": [
          null,
          null,
          null,
          null,
          null,
          null
        ]
      },
      {
        "id": "46KC6K",
        "names": [
          null,
          null,
          null,
          null,
          null,
          null
        ]
      },
      {
        "id": "OC16NE",
        "names": [
          null,
          null,
          null,
          null,
          null
        ]
      },
      {
        "id": "7BFSRI",
        "names": [
          null,
          null,
          null,
          null,
          null,
          null
        ]
      }
    ]
  }
}

I couldn’t find anything about delegation of directives on the apollo doc nor graphql-tool doc, and the dgraph page which lists the directives is still incomplete so I couldn’t find any solution / explanation.

Is that a bug or is it a misconfiguration of the Apollo server?

I would point out that this behaviour occurs only when the directive is used on query, using it on fields works perfectly