Fix IIOB error when dealing with an incomplete YAML && Nagging

By: Erik Broes <erikbroes@grum.nl>

paper-api/src/main/java/org/bukkit/plugin/SimplePluginManager.java

@@ -257,9 +257,14 @@ public final class SimplePluginManager implements PluginManager {
                     Plugin plugin = registration.getPlugin();
                     if (plugin.isNaggable()) {
                         plugin.setNaggable(false);
+
+                        String author = "<NoAuthorGiven>";
+                        if (plugin.getDescription().getAuthors().size() > 0) {
+                            author = plugin.getDescription().getAuthors().get(0); 
+                        }
                         server.getLogger().log(Level.SEVERE, String.format(
                             "Nag author: '%s' of '%s' about the following: %s",
-                            plugin.getDescription().getAuthors().get(0),
+                            author,
                             plugin.getDescription().getName(),
                             ex.getMessage()
                         ));