In an array of plots of regions (inequalities)
p[..] which are eventually combined using
Show, how do I suppress the legend of plots which are empty, and look like this
More generally, if in a given range of $x$ and $y$ over which a region is prescribed to be plotted, if
RegionPlot does not find a solution (so that there is no region to shade or fill), is there a way to get a
False value from RegionPlot corresponding to whether the region exists or not?