default GraphqlErrorHandler orElse(GraphqlErrorHandler other) {
        requireNonNull(other, "other");
        if (this == other) {
            return this;
        }
        return (ctx, input, executionResult, cause) -> {
            final HttpResponse response = handle(ctx, input, executionResult, cause);
            if (response != null) {
                return response;
            }
            return other.handle(ctx, input, executionResult, cause);
        };
    }
Returns a composed {@link GraphqlErrorHandler} that applies this first and the specified
other later if this returns {@code null}.
graphql/src/main/java/com/linecorp/armeria/server/graphql/GraphqlErrorHandler.java