@SuppressWarnings("unchecked")
    private static Map<String, Object> toMapFromJson(@Nullable Object maybeMap) {
        if (maybeMap == null) {
            return ImmutableMap.of();
        }

        if (maybeMap instanceof Map) {
            final Map<?, ?> map = (Map<?, ?>) maybeMap;
            if (map.isEmpty()) {
                return ImmutableMap.of();
            }
            return Collections.unmodifiableMap((Map<String, Object>) maybeMap);
        } else {
            throw new IllegalArgumentException("Unknown parameter type variables");
        }
    }
This only works reliably if maybeMap is from Json, as maps(objects) in Json
can only have string keys.
graphql-protocol/src/main/java/com/linecorp/armeria/server/graphql/protocol/AbstractGraphqlService.java