NoMethodError: undefined method `[]' for nil:NilClass results[:used_fields] = field_usages[:used_fields]

Sentry error: https://new-sentry.gitlab.net/organizations/gitlab/issues/828943

NoMethodError: undefined method `[]' for nil:NilClass

            results[:used_fields] = field_usages[:used_fields]
                                                ^^^^^^^^^^^^^^
  from lib/gitlab/graphql/query_analyzers/ast/logger_analyzer.rb:33:in `result'
  from graphql (2.3.3) lib/graphql/analysis/ast.rb:77:in `map'
  from graphql (2.3.3) lib/graphql/analysis/ast.rb:77:in `block in analyze_query'
  from graphql (2.3.3) lib/graphql/tracing/trace.rb:36:in `analyze_query'
  from graphql (2.3.3) lib/graphql/analysis/ast.rb:52:in `analyze_query'
  from graphql (2.3.3) lib/graphql/analysis/ast.rb:28:in `block (2 levels) in analyze_multiplex'
  from graphql (2.3.3) lib/graphql/analysis/ast.rb:26:in `map'
  from graphql (2.3.3) lib/graphql/analysis/ast.rb:26:in `block in analyze_multiplex'
  from graphql (2.3.3) lib/graphql/tracing/trace.rb:32:in `analyze_multiplex'
  from graphql (2.3.3) lib/graphql/analysis/ast.rb:25:in `analyze_multiplex'
  from graphql (2.3.3) lib/graphql/execution/interpreter.rb:46:in `block in run_all'
  from graphql (2.3.3) lib/graphql/tracing/trace.rb:40:in `execute_multiplex'
  from graphql (2.3.3) lib/graphql/schema/timeout.rb:68:in `execute_multiplex'
  from graphql (2.3.3) lib/graphql/execution/interpreter.rb:37:in `run_all'
  from graphql (2.3.3) lib/graphql/schema.rb:1332:in `multiplex'
  from app/graphql/gitlab_schema.rb:46:in `multiplex'
  from graphql (2.3.3) lib/graphql/schema.rb:1308:in `execute'
  from app/controllers/graphql_controller.rb:226:in `execute_query'
  from app/controllers/graphql_controller.rb:73:in `execute'