I need help with chat

Hi guys, I have a problem with chatview when I try to get the messages from the database

the following message appears

All the data is obtained with total normality, the only problem is the appearance of that message

the strange thing is that the message says about a list of length 1, but when I put a label to get the list length value I get a length of 3 (you can see it in the first image)
Here I leave my blocks, maybe the ones I made are wrong
please help

Sorry for my English, I am using a google translator

These guides can help you:

I made my blocks with the first guide, yes it gets the firebase data, the only problem is the message that comes out