docs: public void addError(GraphQLError error, ExecutionPath fieldPath) {
          //
          // see http://facebook.github.io/graphql/#sec-Errors-and-Non-Nullability about how per
          // field errors should be handled - ie only once per field if its already there for nullability
          // but unclear if its not that error path
          //
          for (GraphQLError graphQLError : errors) {
              List<Object> path = graphQLError.getPath();
              if (path != null) {
                  if (fieldPath.equals(ExecutionPath.fromList(path))) {
                      return;
                  }
              }
          }
          this.errors.add(error);
      }