Spring GraphQL mutation NullPointerException - spring-boot

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": "john#gmail.com",
"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
}

Answer 2

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