The null output plugin just throws away events.
The plugin doesn't support configuration parameters.
You can run the plugin from the command line or through the configuration file:
From the command line you can let Fluent Bit throws away events with the following options:
$ fluent-bit -i cpu -o null
In your main configuration file append the following Input & Output sections:
[INPUT]
Name cpu
Tag cpu
[OUTPUT]
Name null
Match *