nodeplotblank: Function to avoid plotting node labels
Description
Unlike, nodeplotdefault and
nodeplotboot, this function does not return
a function, but instead is provided directly to the
nodelabf argument of plot_tree to
ensure that node labels are not added to the graphic.
Please note that you do not need to create or obtain the
arguments to this function. Instead, you can provide this
function directly to plot_tree and it will
know what to do with it. Namely, use it to avoid plotting
any node labels.