TypeError: 'NoneType' object is not callable
> Hi, @Chenfei-Kang.
> 
> I'm sorry, but I'm not able to reproduce your bug:
> 
> ```python
> from datasets import load_dataset
> 
> ds = load_dataset("glue", 'cola')
> ds
> ```
> 
> ```
> DatasetDict({
>     train: Dataset({
>         features: ['sentence', 'label', 'idx'],
>         num_rows: 8551
>     })
>     validation: Dataset({
>         features: ['sentence', 'label', 'idx'],
>         num_rows: 1043
>     })
>     test: Dataset({
>         features: ['sentence', 'label', 'idx'],
>         num_rows: 1063
>     })
> })
> ```
> 
> Could you please give more details and environment info (platform, PyArrow version)?

Sorry to reply you so late.
platform: pycharm 2021 + anaconda with python 3.7
PyArrow version: 5.0.0
huggingface-hub: 0.0.16
datasets: 1.9.0

## Describe the bug

TypeError: 'NoneType' object is not callable
## Steps to reproduce the bug
```python
from datasets import load_dataset, load_metric
dataset = datasets.load_dataset("glue", 'cola')
```

## Expected results
A clear and concise description of the expected results.

## Actual results
Specify the actual results or traceback.

## Environment info
<!-- You can run the command `datasets-cli env` and copy-and-paste its output below. -->
- `datasets` version: 1.11.0
- Platform:
- Python version: 3.7
- PyArrow version:

TypeError: 'NoneType' object is not callable 
 ## Describe the bug

TypeError: 'NoneType' object is not callable
## Steps to reproduce the bug
```python
from datasets import load_dataset, load_metric
dataset = datasets.load_dataset("glue", 'cola')
```

## Expected results
A clear and concise description of the expected results.

## Actual results
Specify the actual results or traceback.

## Environment info
<!-- You can run the command `datasets-cli env` and copy-and-paste its output below. -->
- `datasets` version: 1.11.0
- Platform:
- Python version: 3.7
- PyArrow version:
 
 > Hi, @Chenfei-Kang.
> 
> I'm sorry, but I'm not able to reproduce your bug:
> 
> ```python
> from datasets import load_dataset
> 
> ds = load_dataset("glue", 'cola')
> ds
> ```
> 
> ```
> DatasetDict({
>     train: Dataset({
>         features: ['sentence', 'label', 'idx'],
>         num_rows: 8551
>     })
>     validation: Dataset({
>         features: ['sentence', 'label', 'idx'],
>         num_rows: 1043
>     })
>     test: Dataset({
>         features: ['sentence', 'label', 'idx'],
>         num_rows: 1063
>     })
> })
> ```
> 
> Could you please give more details and environment info (platform, PyArrow version)?

Sorry to reply you so late.
platform: pycharm 2021 + anaconda with python 3.7
PyArrow version: 5.0.0
huggingface-hub: 0.0.16
datasets: 1.9.0
