graphQLSchema Empty After Upgrading to Serverless Framework v4

[ugurhicyilmam]

After upgrading from Serverless Framework v3.x to v4, the serverless-appsync-plugin is encountering an issue where the graphQLSchema is empty upon deployment. Reverting to v3.x resolves the problem, indicating a potential compatibility issue between the plugin and the latest version of the Serverless Framework.

Steps to Reproduce:

• Upgrade Serverless Framework to version 4.x (tested on versions ranging from 4.3.3 to 4.4.18).
• Deploy a service configured with serverless-appsync-plugin and a defined GraphQL schema.
• Observe that the deployed AppSync API has an empty schema, and deployment fails with an error: "Definition cannot be empty."

Expected Behavior:
The GraphQL schema should deploy correctly, as it does with Serverless Framework v3.x.

Actual Behavior:
The deployed AppSync API has an empty graphQLSchema, and deployment fails with the error mentioned above.

What I’ve Tried:

• Tested with multiple Serverless Framework v4 versions, from 4.3.3 to 4.4.18 (latest), with no success.
• Test with multiple serverless-appsync versions from 2.7.0 to 2.9.1, with no success.
• Simplified the GraphQL schema to the following minimal example:

type Mutation {
    addTodo(pk: String!, input: TodoInput!): ToDo!
}


type Query {
    getTodo(pk: String!, sk: String!): ToDo
}

type ToDo {
    pk: String!
    sk: String!
    val: String!
}

input TodoInput {
    val: String!
}

The issue persists even with this simple schema.
Simplified the configuration to the bare minimum:

custom:
  appSync:
    name: 'api'
    schema: 'schema.graphql'
    authentication:
      type: 'AMAZON_COGNITO_USER_POOLS'
      config:
        userPoolId:
          Ref: 'CognitoUserPool'

The issue persists with this minimal configuration.
Validated the schema using the validate-schema command, which works fine without errors.
Checked the generated package; the schema definition is missing, indicating it is not being bundled correctly during deployment.