ConfigKeyError: str interpolation key 'model.language_model.pretrained_model_name' not found
State: closed | Pull request: no
Labels: name: bug

I'm trying to reproduce [Named Entity Recognition - BioMegatron colab](https://colab.research.google.com/github/NVIDIA/NeMo/blob/r1.0.0b3/tutorials/nlp/Token_Classification-BioMegatron.ipynb), everything is fine until the following cell:

`model_ner = nemo_nlp.models.TokenClassificationModel(cfg=config.model, trainer=trainer)`

Output:
```
[NeMo I 2021-01-06 10:36:00 megatron_utils:235] Downloading from https://api.ngc.nvidia.com/v2/models/nvidia/biomegatron345mcased/versions/0/files/vocab.txt
Downloading: 100%
625/625 [00:00<00:00, 1.31kB/s]

Downloading: 100%
213k/213k [00:00<00:00, 3.31MB/s]
Using bos_token, but it is not set yet.
Using eos_token, but it is not set yet.

---------------------------------------------------------------------------
ConfigKeyError                            Traceback (most recent call last)
<ipython-input-25-4645443f78bc> in <module>()
----> 1 model_ner = nemo_nlp.models.TokenClassificationModel(cfg=config.model, trainer=trainer)

8 frames
/usr/local/lib/python3.6/dist-packages/omegaconf/base.py in _resolve_simple_interpolation(self, key, inter_type, inter_key, throw_on_missing, throw_on_resolution_failure)
    326                 if throw_on_resolution_failure:
    327                     raise ConfigKeyError(
--> 328                         f"{inter_type} interpolation key '{inter_key}' not found"
    329                     )
    330                 else:

ConfigKeyError: str interpolation key 'model.language_model.pretrained_model_name' not found
```

I believe that `config.model.language_model.pretrained_model_name = 'biomegatron-bert-345m-cased'`. In addition, I'm getting an error in the installation phase though I'm not sure it would be related to this issue:

```
# install NeMo
BRANCH = 'main'
!python -m pip install git+https://github.com/NVIDIA/NeMo.git@$BRANCH#egg=nemo_toolkit[nlp]
```

Output:
```
Collecting nemo_toolkit[nlp]
  Cloning https://github.com/NVIDIA/NeMo.git (to revision main) to /tmp/pip-install-hz__8v6m/nemo-toolkit
  Running command git clone -q https://github.com/NVIDIA/NeMo.git /tmp/pip-install-hz__8v6m/nemo-toolkit
Requirement already satisfied: numpy>=1.18.2 in /usr/local/lib/python3.6/dist-packages (from nemo_toolkit[nlp]) (1.19.4)
...
Successfully built nemo-toolkit wget future PyYAML antlr4-python3-runtime sacremoses idna-ssl
ERROR: albumentations 0.1.12 has requirement imgaug<0.2.7,>=0.2.5, but you'll have imgaug 0.2.9 which is incompatible.
ERROR: botocore 1.19.49 has requirement urllib3<1.27,>=1.25.4; python_version != "3.4", but you'll have urllib3 1.24.3 which is incompatible.
Installing collected packages: onnx, multidict, yarl, async-timeout, idna-ssl, aiohttp, fsspec, future, PyYAML, pytorch-lightning, wget, ruamel.yaml.clib, ruamel.yaml, omegaconf, antlr4-python3-runtime, hydra-core, sacremoses, tokenizers, transformers, sentencepiece, typer, braceexpand, simplejson, objectio, webdataset, jmespath, botocore, s3transfer, boto3, matplotlib, unidecode, youtokentome, rapidfuzz, pybind11, megatron-lm, nemo-toolkit
  Found existing installation: future 0.16.0
    Uninstalling future-0.16.0:
      Successfully uninstalled future-0.16.0
  Found existing installation: PyYAML 3.13
    Uninstalling PyYAML-3.13:
      Successfully uninstalled PyYAML-3.13
  Found existing installation: matplotlib 3.2.2
    Uninstalling matplotlib-3.2.2:
      Successfully uninstalled matplotlib-3.2.2
Successfully installed PyYAML-5.3.1 aiohttp-3.7.3 antlr4-python3-runtime-4.8 async-timeout-3.0.1 boto3-1.16.49 botocore-1.19.49 braceexpand-0.1.6 fsspec-0.8.5 future-0.18.2 hydra-core-1.0.4 idna-ssl-1.1.0 jmespath-0.10.0 matplotlib-3.3.3 megatron-lm-1.1.5 multidict-5.1.0 nemo-toolkit-1.0.0b4 objectio-0.2.29 omegaconf-2.0.5 onnx-1.8.0 pybind11-2.6.1 pytorch-lightning-1.1.3 rapidfuzz-0.14.2 ruamel.yaml-0.16.12 ruamel.yaml.clib-0.2.2 s3transfer-0.3.3 sacremoses-0.0.43 sentencepiece-0.1.94 simplejson-3.17.2 tokenizers-0.9.4 transformers-4.1.1 typer-0.3.2 unidecode-1.1.2 webdataset-0.1.40 wget-3.2 yarl-1.6.3 youtokentome-1.0.6
```