Resolving a field that references a Type in another subgraph

So, here’s my stack:

Customers subgraph running on Django, python, graphene-federation.

  • Has a CustomerType that is linked to a Customer model

Sprints subgraph running on Django, python, graphene-federation.

  • Has a SprintType that is linked to a Sprint model
  • The SprintType has a field called “customer” that holds a UUID to a Customer in the Customers service.

My question is:
How would I make sure that the “customer” field in the SprintType is being resolved within the Customers subgraph?

Here’s the query I am trying to run:

query Query {
  allSprints {
    customer {

Here’s the error code:

  "data": {
    "allSprints": [
        "customer": null
  "errors": [
      "message": "Cannot return null for non-nullable field",
      "path": [
      "extensions": {
        "serviceName": "customers",
        "stacktrace": [
          "GraphQLError: Cannot return null for non-nullable field",
          "    at Object.err (D:\\Tailored Software\\Sprints\\5-2023\\Repos\\graphql-server-example\\node_modules\\@apollo\\federation-internals\\dist\\error.js:11:32)",
          "    at downstreamServiceError (D:\\Tailored Software\\Sprints\\5-2023\\Repos\\graphql-server-example\\node_modules\\@apollo\\gateway\\dist\\executeQueryPlan.js:585:120)",
          "    at D:\\Tailored Software\\Sprints\\5-2023\\Repos\\graphql-server-example\\node_modules\\@apollo\\gateway\\dist\\executeQueryPlan.js:309:59",
          "    at (<anonymous>)",
          "    at sendOperation (D:\\Tailored Software\\Sprints\\5-2023\\Repos\\graphql-server-example\\node_modules\\@apollo\\gateway\\dist\\executeQueryPlan.js:309:44)",
          "    at processTicksAndRejections (node:internal/process/task_queues:96:5)",
          "    at async D:\\Tailored Software\\Sprints\\5-2023\\Repos\\graphql-server-example\\node_modules\\@apollo\\gateway\\dist\\executeQueryPlan.js:256:49",
          "    at async executeNode (D:\\Tailored Software\\Sprints\\5-2023\\Repos\\graphql-server-example\\node_modules\\@apollo\\gateway\\dist\\executeQueryPlan.js:180:17)",
          "    at async executeNode (D:\\Tailored Software\\Sprints\\5-2023\\Repos\\graphql-server-example\\node_modules\\@apollo\\gateway\\dist\\executeQueryPlan.js:171:27)",
          "    at async executeNode (D:\\Tailored Software\\Sprints\\5-2023\\Repos\\graphql-server-example\\node_modules\\@apollo\\gateway\\dist\\executeQueryPlan.js:154:40)"

I forgot to mention: I am also using Apollo Gateway that combines these services’ subgraphs into a supergraph for federation.