code: @Override
      public List<Map<String, Object>> get (DataFetchingEnvironment environment) {
          // GetSource is the context in which this this DataFetcher has been created, in this case a map representing
          // the parent feed (FeedFetcher).
          Map<String, Object> parentEntityMap = environment.getSource();
  
          // Apparently you can't get the arguments from the parent - how do you have arguments on sub-fields?
          // It looks like you have to redefine the argument on each subfield and pass it explicitly in the GraphQL request.
  
          // String namespace = environment.getArgument("namespace"); // This is going to be the unique prefix, not the feedId in the usual sense
          // This DataFetcher only makes sense when the enclosing parent object is a feed or something in a feed.
          // So it should always be represented as a map with a namespace key.
  
          String namespace = (String) parentEntityMap.get("namespace");
  
          // If we are fetching an item nested within a GTFS entity in the GraphQL query, we want to add an SQL "where"
          // clause using the values found here. Note, these are used in the below getResults call.
          List<String> parentJoinValues = new ArrayList<>();
          if (parentJoinField != null) {
              Map<String, Object> enclosingEntity = environment.getSource();
              // FIXME: THIS IS BROKEN if parentJoinValue is null!!!!
              Object parentJoinValue = enclosingEntity.get(parentJoinField);
              // Check for null parentJoinValue to protect against NPE.
              String parentJoinString = parentJoinValue == null ? null : parentJoinValue.toString();
              parentJoinValues.add(parentJoinString);
              if (parentJoinValue == null) {
                  return new ArrayList<>();
              }
          }
          Map<String, Object> arguments = environment.getArguments();
  
          return getResults(namespace, parentJoinValues, arguments);
      }
docs: But what are the internal GraphQL objects, i.e. what does an ExecutionResult return? Are they Map<String, Object>?