Spring GraphQL mutation NullPointerException

Question

I'm learning GraphQL in spring boot and I have created a mutation that saves used details in database. When I try to call the mutation from GraphiQL UI using following mutation query, it throws NullPointerException because the object I passed in mutation is not mapped with UserDto and I don't know why.

I have following code:

Controller

@Controller
public class UserController {

    private UserService userService;


    public UserController(UserService userService) {
        this.userService = userService;
    }

    @QueryMapping(name = "userById")
    public UserDto findUserById(@Argument Long id) {
        return userService.findById(id);
    }

    @QueryMapping
    public String removeUserById(@Argument Long id) {
        return userService.removeById(id);
    }

    @MutationMapping(name = "save")
    public UserDto save(@Argument UserDto user) {
        return  userService.save(user);
    }

    @QueryMapping(name = "users")
    public List<UserDto> findAll() {
        return userService.findAll();
    }

}

GraphQL Schema

schema {
    query: Query
    mutation: Mutation
}


type Query{
    users:[User]
    userById(id:ID):User
}
type Mutation{
    save(userInput:UserInput):User
}

#input types
input UserInput{
    firstName:String!
    lastName:String!
    emailAddress:String!
    ipAddress:String!
    address:AddressInput!
}
input AddressInput{
    addressLine1:String!
    addressLine2:String!
    addressLine3:String!
    addressLine4:String!
    addressLine5:String!
    addressPostCode:Int!
}

#object types
type User{
    firstName:String!
    lastName:String!
    emailAddress:String!
    ipAddress:String!
    address:Address!
}
type Address{
    addressLine1:String!
    addressLine2:String!
    addressLine3:String!
    addressLine4:String!
    addressLine5:String!
    addressPostCode:Int!
}

Mutation Query

mutation Save($userDto: UserInput!) {
  save(userInput: $userDto) {
    firstName
    lastName
    emailAddress
    ipAddress
    address {
      addressLine1
      addressLine2
      addressLine3
      addressLine4
      addressLine5
      addressPostCode
    }
  }
}

Variables

{
  "userDto": {
    "ipAddress": "192.168.0.124",
    "firstName": "John",
    "lastName": "Mark",
    "emailAddress": "[email protected]",
    "address": {
      "addressLine1": "251 WC",
      "addressLine2": "UC MAIN",
      "addressLine3": "PB121",
      "addressLine4": "New York",
      "addressLine5": "USA",
      "addressPostCode": 457821
    }
  }
}

Results

{
  "errors": [
    {
      "message": "INTERNAL_ERROR for b6287602-fc10-6ecf-2091-b57ceaeb9f0a",
      "locations": [
        {
          "line": 2,
          "column": 3
        }
      ],
      "path": [
        "save"
      ],
      "extensions": {
        "classification": "INTERNAL_ERROR"
      }
    }
  ],
  "data": {
    "save": null
  }
}

When I run the GraphQL query, it throws NullPointerException in console.

Console Error

java.lang.NullPointerException: Cannot invoke "com.graphql.sample.dto.UserDto.getEmailAddress()" because "userDto" is null

Answer 1

I'm answering my question because I have already solved it. I had made a small mistake in controller near @Argument UserDto user as below:

@MutationMapping(name = "save")
public UserDto save(@Argument(name = "userInput") UserDto user) {
        return  userService.save(user);
}

The name in @Argument should match the name of parameter in Mutation type as below:

type Mutation{
    save(userInput:UserInput):User
}