Considering this schema:

type Query {
  search(filters: SearchFilters = { pageSize: 20 }): [Result!]!
}

input SearchFilters {
  pageSize: Int!
}

type Result {
  id: ID!
}

Where pageSize's out_name is page_size, when no custom pageSize value is included in query, the resolver is called with {"pageSize": 20} kwarg, resulting in Python error in query execution.