fix for fast/slow tokenizers compatibility
This pull request **fixes 1 alert** when merging 8ad7e9a62e964dcab1adc45a20f76b4bf09347d3 into e54a3b030e11bcc64327e10bed7ea70724651260 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-656a0fc1adcb486ec3bbd4aec5fbac97896b62f7)

**fixed alerts:**

* 1 for Unused import This pull request **fixes 1 alert** when merging d48d9f0e34cb7174c68bcc63ee4be0e556dbe361 into e54a3b030e11bcc64327e10bed7ea70724651260 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-49a1ec54d0073b27936b6de1a4379124e8936a00)

**fixed alerts:**

* 1 for Unused import
Signed-off-by: ekmb <ebakhturina@nvidia.com>