Can't use Fluentd with the "fluent-plugin-sql" plugin

Question

I want to use fluentd to read data from a database in a dockerized environment. In the container where I have installed fluentd I put this "fluent.conf" file:

<source>
  @type sql
  host db
  port 3306
  database logs-db
  adapter mysql2
  username john
  password johnpassword
  tag_prefix docker.logify  # optional, but recommended
  state_file /var/run/fluentd/sql_state
  <table>
    table logs-tb
    update_column id
  </table>
</source>

<match docker.logify>
  @type file
  path /fluentd/etc/logs/docker.logify.log
</match>

The problem is that when I start the container I get these errors:

2024-02-23 11:00:39 +0000 [error]: #0 unexpected error error_class=NoMethodError error="undefined method `exists?' for File:Class"
2024-02-23 11:00:39 +0000 [error]: #0 /usr/local/lib/ruby/gems/3.2.0/gems/fluent-plugin-sql-2.3.0/lib/fluent/plugin/in_sql.rb:285:in `initialize'
2024-02-23 11:00:39 +0000 [error]: #0 /usr/local/lib/ruby/gems/3.2.0/gems/fluent-plugin-sql-2.3.0/lib/fluent/plugin/in_sql.rb:186:in `new'
2024-02-23 11:00:39 +0000 [error]: #0 /usr/local/lib/ruby/gems/3.2.0/gems/fluent-plugin-sql-2.3.0/lib/fluent/plugin/in_sql.rb:186:in `start'
2024-02-23 11:00:39 +0000 [error]: #0 /usr/local/lib/ruby/gems/3.2.0/gems/fluentd-1.16.3/lib/fluent/root_agent.rb:203:in `block in start'
2024-02-23 11:00:39 +0000 [error]: #0 /usr/local/lib/ruby/gems/3.2.0/gems/fluentd-1.16.3/lib/fluent/root_agent.rb:192:in `block (2 levels) in lifecycle'

The fluent-plugin-sql plugin seems to be installed properly, because when I do

fluent-gem list | grep fluent-plugin-sql

I get

fluent-plugin-sql (2.3.0)