docs: public GraphQLObjectType getObjectType(String typeName) {
          GraphQLType graphQLType = typeMap.get(typeName);
          if (graphQLType != null) {
              assertTrue(graphQLType instanceof GraphQLObjectType,
                      format("You have asked for named object type '%s' but its not an object type but rather a '%s'", typeName, graphQLType.getClass().getName()));
          }
          return (GraphQLObjectType) graphQLType;
      }