Oh… Well, this is my trainer:
trainer = Trainer(
    model=model,
    args=training_args,
    train_dataset=lm_datasets["train"],
    eval_dataset=lm_datasets["test"],
    data_collator=data_collator,
)

I thought the data_collator contains the tokenizer?
Like, here, for example:
from transformers import DataCollatorForLanguageModeling
data_collator = DataCollatorForLanguageModeling(tokenizer=tokenizer, mlm_probability=0.15)