Generally, yes—leaving a camera battery charger plugged in with no battery installed should not harm the charger. Most chargers draw a small amount of standby power even when they are not actively charging, but that idle draw is usually minimal and not considered damaging by itself.

So the main tradeoff is efficiency, not charger wear: if you leave it plugged in, it may waste a little electricity. If you want to save power, unplug it or switch it off when not in use.

As with any mains-powered device, normal common-sense safety still applies: use the charger in good condition, keep it dry, and avoid damaged cables or outlets. But based on the answers here, simply leaving it plugged in without a battery is not considered harmful.