@carlos-conde Welcome to the forum!
- what version of NR and node.js are you running? (you can find this in the startup log)
- what platform are you running NR on?
I did a copy of the data you say is causing the error and sent it thru a json node and it had no problem with it.
Please create a small flow demonstrating your issue and then export it and attach it to a reply.
In order to make code readable and usable it is necessary to surround your code with three backticks (also known as a left quote or backquote ```)
```
code goes here
```
You can edit and correct your post by clicking the pencil 
icon.
See this post for more details - How to share code or flow json
