public GsonGrpcJsonMarshallerBuilder jsonParserCustomizer(
            Function<? super JsonFormat.Parser, JsonFormat.Parser> jsonParserCustomizer) {
        requireNonNull(jsonParserCustomizer, "jsonParserCustomizer");
        if (this.jsonParserCustomizer == null) {
            @SuppressWarnings("unchecked")
            final Function<JsonFormat.Parser, JsonFormat.Parser> cast =
                    (Function<JsonFormat.Parser, JsonFormat.Parser>) jsonParserCustomizer;
            this.jsonParserCustomizer = cast;
        } else {
            this.jsonParserCustomizer = this.jsonParserCustomizer.andThen(jsonParserCustomizer);
        }
        return this;
    }
Adds a {@link Function} that returns customized the {@link JsonFormat.Parser}
used when deserializing a JSON payload into a {@link Message}.
grpc/src/main/java/com/linecorp/armeria/common/grpc/GsonGrpcJsonMarshallerBuilder.java