Query:
{
fetch(arg: {
User: {
id: 38710
}
}){
data
}
}

debug:
[nio-8080-exec-2] graphql.GraphQL : Query failed to parse : '{"operationName":null,"variables":{},"query":"{\n fetch(arg: {User: {id: 38710}}) {\n data\n }\n}\n"}'

result:
{
"errors": [
{
"message": "Invalid Syntax",
"locations": [
{
"line": 1,
"column": 1
}
]
}
]
}