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

Amit-Chavda · Accepted Answer · 2022-07-26 13:44:04Z

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 }

Aayush Jain · Accepted Answer · 2022-07-26 11:11:29Z

type User{ firstName:String! lastName:String! emailAddress:String! ipAddress:String! address:Address! }

Reason 1: Your save mutation result is returned to this entity. But it can be possible that a property that you are receiving might be null that's why this error is thrown, as you are using ! with each property. You can remove ! if a value can/is null

Reason 2: I couldn't see your resolver so it might be possible that the result is not an object or the property names that you are receiving don't match with the property names inside type User. It should be same or use resolver to provide their values

Getting error in controller saying the @Argument UserDto user is Null. I mean user passed as argument in mutation is null even if i have passed value stored in variable.
And is resolver mandatory even if I use @MutationMapping annotation to map graphql mutation with method?

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