Allow the user to remove the subtitle in plots

[hbaniecki]

At this moment, plot functions with the subtitle parameter have it set to NULL as default.

Therefore, it is not possible for the user to remove the subtitle using the conventional subtitle=NULL value.

Perhaps set a different default value? It is clearly not NULL, because the subtitle appears by deafult.

survex/R/plot_surv_feature_importance.R

Lines 73 to 76 in 561b62e

	if (is.null(subtitle)) {
	glm_labels <- paste0(label, collapse = ", ")
	subtitle <- paste0("created for the ", glm_labels, " model")
	}

[mikolajsp]

You can set it to "" for no subtitle but I agree NULL as default parameter isn't the best option.

[hbaniecki]

"" creates a margin between the title and plot.