Regressors in estimating trend and seasonality

[gferrandik]

I am interested in understanding how seasonality and trend are computed in Robyn. As far as I understood from another discussion, raw media, context variables and organic variables are added as regressors in Prophet model before fitting.

However, when I read the code here, in the prophet_decomp function, it seems to me that regressors are added only when factor_vars are present in the dataset, via add_regressor, and they are added only if they are encoded factor variables. Am I missing something?

Thank you for your time and work.