Object invoke(String methodName, Object argument, Type returnType) throws Throwable {
    try {
      return invokeAsync(methodName, argument, returnType).join();
    } catch (CompletionException ex) {
      // Unwrap CompletionExceptions as normal exceptions
      throw ex.getCause();
    }
  }
Invoke a JSON-RPC method synchronously without compile-time type-checking.

<p>This overload is package-private, because it should only be used by the {@link
JsonRpcLambdaProxyAdapter} (which requires a non-typesafe invoke method).
json-rpc-lambda-client/src/main/java/com/amazonaws/blox/jsonrpc/JsonRpcLambdaClient.java