Bug: relations are lost when using sparse fieldset combined with include

[bart-degreed]

When using sparse fieldsets, any related data that is included will be set to null.

For example, request to http://localhost:1479/api/v1/todoItems/375?include=owner returns:

{
  "links": {
    "self": "http://localhost:1479/api/v1/todoItems/375"
  },
  "data": {
    "type": "todoItems",
    "id": "375",
    "attributes": {
      "description": "Iusto harum voluptatem voluptatibus asperiores est iusto architecto eaque numquam.",
      "ordinal": 1,
      "guidProperty": "e0ca07d8-3db2-4060-a6d8-a910b0a1e672",
      "createdDate": "2019-11-08T06:59:38.612382",
      "achievedDate": null,
      "updatedDate": null,
      "calculatedValue": "calculated",
      "offsetDate": null
    },
    "relationships": {
      "owner": {
        "links": {
          "self": "http://localhost:1479/api/v1/todoItems/375/relationships/owner",
          "related": "http://localhost:1479/api/v1/todoItems/375/owner"
        },
        "data": {
          "type": "people",
          "id": "129"
        }
      },
      "assignee": {
        "links": {
          "self": "http://localhost:1479/api/v1/todoItems/375/relationships/assignee",
          "related": "http://localhost:1479/api/v1/todoItems/375/assignee"
        }
      },
      "oneToOnePerson": {
        "links": {
          "self": "http://localhost:1479/api/v1/todoItems/375/relationships/oneToOnePerson",
          "related": "http://localhost:1479/api/v1/todoItems/375/oneToOnePerson"
        }
      },
      "stakeHolders": {
        "links": {
          "self": "http://localhost:1479/api/v1/todoItems/375/relationships/stakeHolders",
          "related": "http://localhost:1479/api/v1/todoItems/375/stakeHolders"
        }
      },
      "collection": {
        "links": {
          "self": "http://localhost:1479/api/v1/todoItems/375/relationships/collection",
          "related": "http://localhost:1479/api/v1/todoItems/375/collection"
        }
      },
      "dependentOnTodo": {
        "links": {
          "self": "http://localhost:1479/api/v1/todoItems/375/relationships/dependentOnTodo",
          "related": "http://localhost:1479/api/v1/todoItems/375/dependentOnTodo"
        }
      },
      "parentTodo": {
        "links": {
          "self": "http://localhost:1479/api/v1/todoItems/375/relationships/parentTodo",
          "related": "http://localhost:1479/api/v1/todoItems/375/parentTodo"
        }
      },
      "childrenTodos": {
        "links": {
          "self": "http://localhost:1479/api/v1/todoItems/375/relationships/childrenTodos",
          "related": "http://localhost:1479/api/v1/todoItems/375/childrenTodos"
        }
      }
    },
    "links": {
      "self": "http://localhost:1479/api/v1/todoItems/375"
    }
  },
  "included": [
    {
      "type": "people",
      "id": "129",
      "attributes": {
        "firstName": "Tiffany",
        "lastName": "Kub",
        "age": 97
      },
      "relationships": {
        "todoItems": {
          "links": {
            "self": "http://localhost:1479/api/v1/people/129/relationships/todoItems",
            "related": "http://localhost:1479/api/v1/people/129/todoItems"
          }
        },
        "assignedTodoItems": {
          "links": {
            "self": "http://localhost:1479/api/v1/people/129/relationships/assignedTodoItems",
            "related": "http://localhost:1479/api/v1/people/129/assignedTodoItems"
          }
        },
        "todoCollections": {
          "links": {
            "self": "http://localhost:1479/api/v1/people/129/relationships/todoCollections",
            "related": "http://localhost:1479/api/v1/people/129/todoCollections"
          }
        },
        "role": {
          "links": {
            "self": "http://localhost:1479/api/v1/people/129/relationships/role",
            "related": "http://localhost:1479/api/v1/people/129/role"
          }
        },
        "oneToOneTodoItem": {
          "links": {
            "self": "http://localhost:1479/api/v1/people/129/relationships/oneToOneTodoItem",
            "related": "http://localhost:1479/api/v1/people/129/oneToOneTodoItem"
          }
        },
        "stakeHolderTodoItem": {
          "links": {
            "self": "http://localhost:1479/api/v1/people/129/relationships/stakeHolderTodoItem",
            "related": "http://localhost:1479/api/v1/people/129/stakeHolderTodoItem"
          }
        },
        "unIncludeableItem": {
          "links": {
            "self": "http://localhost:1479/api/v1/people/129/relationships/unIncludeableItem",
            "related": "http://localhost:1479/api/v1/people/129/unIncludeableItem"
          }
        },
        "passport": {
          "links": {
            "self": "http://localhost:1479/api/v1/people/129/relationships/passport",
            "related": "http://localhost:1479/api/v1/people/129/passport"
          }
        }
      },
      "links": {
        "self": "http://localhost:1479/api/v1/people/129"
      }
    }
  ]
}

But request to http://localhost:1479/api/v1/todoItems/375?include=owner&fields=description returns:

{
  "links": {
    "self": "http://localhost:1479/api/v1/todoItems/375"
  },
  "data": {
    "type": "todoItems",
    "id": "375",
    "attributes": {
      "description": "Iusto harum voluptatem voluptatibus asperiores est iusto architecto eaque numquam."
    },
    "relationships": {
      "owner": {
        "links": {
          "self": "http://localhost:1479/api/v1/todoItems/375/relationships/owner",
          "related": "http://localhost:1479/api/v1/todoItems/375/owner"
        },
        "data": null
      },
      "assignee": {
        "links": {
          "self": "http://localhost:1479/api/v1/todoItems/375/relationships/assignee",
          "related": "http://localhost:1479/api/v1/todoItems/375/assignee"
        }
      },
      "oneToOnePerson": {
        "links": {
          "self": "http://localhost:1479/api/v1/todoItems/375/relationships/oneToOnePerson",
          "related": "http://localhost:1479/api/v1/todoItems/375/oneToOnePerson"
        }
      },
      "stakeHolders": {
        "links": {
          "self": "http://localhost:1479/api/v1/todoItems/375/relationships/stakeHolders",
          "related": "http://localhost:1479/api/v1/todoItems/375/stakeHolders"
        }
      },
      "collection": {
        "links": {
          "self": "http://localhost:1479/api/v1/todoItems/375/relationships/collection",
          "related": "http://localhost:1479/api/v1/todoItems/375/collection"
        }
      },
      "dependentOnTodo": {
        "links": {
          "self": "http://localhost:1479/api/v1/todoItems/375/relationships/dependentOnTodo",
          "related": "http://localhost:1479/api/v1/todoItems/375/dependentOnTodo"
        }
      },
      "parentTodo": {
        "links": {
          "self": "http://localhost:1479/api/v1/todoItems/375/relationships/parentTodo",
          "related": "http://localhost:1479/api/v1/todoItems/375/parentTodo"
        }
      },
      "childrenTodos": {
        "links": {
          "self": "http://localhost:1479/api/v1/todoItems/375/relationships/childrenTodos",
          "related": "http://localhost:1479/api/v1/todoItems/375/childrenTodos"
        }
      }
    },
    "links": {
      "self": "http://localhost:1479/api/v1/todoItems/375"
    }
  }
}

Note how data.relationships.owner.data has been set to null in the second response.