regressor_coefficients not finding regr_names

Make a model; add a regressor; fit the model
`m <- prophet(seasonality.mode = "multiplicative")`

`z<- add_regressor(m, "enr")`

`z<- fit.prophet(z, y)`

Call regressor_coefficients()
`regressor_coefficients(m = z)`

Returns
Error in which(m$train.component.cols[, regr_names] == 1, arr.ind = TRUE)[, :
incorrect number of dimensions

m$train.components.cols is missing a regr_names field that it wants here