Make sure the plugins folder actually exists before iterating

ProtocolLib/src/main/java/com/comphenix/protocol/ProtocolLibrary.java

@@ -501,6 +501,8 @@ public class ProtocolLibrary extends JavaPlugin {
 			// The plugin folder isn't always plugins/
 			File pluginFolder = getDataFolder().getParentFile();
 
+			File[] candidates = pluginFolder.listFiles();
+			if (candidates != null) {
 				for (File candidate : pluginFolder.listFiles()) {
 					if (candidate.isFile() && !candidate.equals(loadedFile)) {
 						Matcher match = ourPlugin.matcher(candidate.getName());
@@ -516,6 +518,7 @@ public class ProtocolLibrary extends JavaPlugin {
 						}
 					}
 				}
+			}
 		} catch (Exception e) {
 			// TODO This shows [ProtocolLib] and [ProtocolLibrary] in the message
 			reporter.reportWarning(this, Report.newBuilder(REPORT_CANNOT_DETECT_CONFLICTING_PLUGINS).error(e));