Appsync returns null values

Here’s the relevant schema definitions:

type Course implements GrApp {
    id: ID!
    term_id: ID!
    term_name: String
    type: String!
    name: String!
    data: AWSJSON
    course_info: AWSJSON
}

interface GrApp {
    id: ID!
    type: String!
    name: String!
    data: AWSJSON
}

input TableGrAppFilterInput {
    id: TableIDFilterInput
    type: TableStringFilterInput
    name: TableStringFilterInput
}

input TableIDFilterInput {
    ne: ID
    eq: ID
    le: ID
    lt: ID
    ge: ID
    gt: ID
    contains: ID
    notContains: ID
    between: [ID]
    beginsWith: ID
}

input TableIntFilterInput {
    ne: Int
    eq: Int
    le: Int
    lt: Int
    ge: Int
    gt: Int
    contains: Int
    notContains: Int
    between: [Int]
}

input TableStringFilterInput {
    ne: String
    eq: String
    le: String
    lt: String
    ge: String
    gt: String
    contains: String
    notContains: String
    between: [String]
    beginsWith: String
}

type Term implements GrApp {
    id: ID!
    type: String!
    name: String!
    data: AWSJSON
    courses: [Course]
}

type Query {
    allTerm(filter: TableGrAppFilterInput, limit: Int, nextToken: String): TermConnection
}

An explanation of my schema: I have an interface/base of GrApp, and then Course and Term implementing it. This is because I have one DynamoDB database representing all my data (it’s just easier this way) and I have both a primary key (id) and a sort key (type) that differentiates between these two types.

However, I’m having trouble with the allTerm query. This is my resolver:

import { util } from '@aws-appsync/utils';

export function request(ctx) {
  const type="term";
  const { limit = 20, nextToken } = ctx.arguments;
  const index = 'type-index';
  const query = JSON.parse(
    util.transform.toDynamoDBConditionExpression({ type: { eq: type } })
  );
  return { operation: 'Query', index, query, limit, nextToken };
}

export function response(ctx) {
  const { items: posts = [], nextToken } = ctx.result;
  return { posts, nextToken };
}

With this query:

query listGrApps {
  allTerm {
    items {
      id
      name
    }
  }
}

Gives me this:

{
  "data": {
    "allTerm": {
      "items": null
    }
  }
}

I got the above resolver code from https://docs.aws.amazon.com/appsync/latest/devguide/tutorial-dynamodb-resolvers-js.html#configure-query (the allPostsByAuthor resolver part)

I’m not too sure why this is not working.