Error 500 on non-assigned variables

[itadventurer]

Example: Heros

Query:

query speciess($filter: SpeciesFilter){
  Speciess(filter: $filter){
    id
    name
    heros {
      id
      heroName
    }
  }
}

Variables: None

Expected result: the same as without mentioning the filter at all. Result: Error 500