public ClientPreprocessorsBuilder addRpc(RpcPreprocessor rpcPreprocessor) {
        rpcPreprocessors.add(requireNonNull(rpcPreprocessor, "rpcPreprocessor"));
        return this;
    }
Adds the specified RPC-level {@code preprocessor}.

@param rpcPreprocessor the {@link HttpPreprocessor} that preprocesses an invocation
core/src/main/java/com/linecorp/armeria/client/ClientPreprocessorsBuilder.java