Tabular data using dataframe: "your generator is empty"

I have created data loaders using a dataframe. There is a path parameter in the API. I do not understand what this parameter should be set to and what the meaning of it is.

to = TabularDataLoaders.from_df(df_ml, path='.', procs=procs, cat_names=cat_names, cont_names=cont_names, y_names="miles", splits=splits)
dls = to.dataloaders(bs=64)

I get a this warning when I start training:
UserWarning: Your generator is empty. warn("Your generator is empty.")