[Python] What is the meaning of Data variables: *empty* in working with .nc file

I had the task of analysing a .nc file. I have not worked with it before now, so I did some research online and found some codes. I was exploring the dataset. I tried:

I am using debian 12, python3 and jupyter notebook

# import needed libraries
import numpy as np

import xarray as xr

# import dataset
file_path = 'dataset/air_quality.nc'

xrds = xr.open_dataset(file_path)

xrds


I saw it printed

Dimensions:

Coordinates: (0)

Data variables: (0)

Indexes: (0)

Attributes: (52)

Down the line, I ran the following code:

xrds.data_vars

Output:
Data variables:
*empty*


Please does it mean that the dataset contains no variables or values I can explore? Thanks in advance.

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