Version is 0.9.13b (BETA) for now! So I see it is quite stable. Before release I have to implement the least of Vault methods.

* Attention about old WorldGuard version.
* Pretty format for debug info.
* getGroups() returns in normal letter case.

pom.xml

@@ -4,7 +4,7 @@
 
 	<groupId>ru.simsonic</groupId>
 	<artifactId>rscPermissions</artifactId>
-	<version>0.9.12a</version>
+	<version>0.9.13b</version>
 	<packaging>jar</packaging>
 
 	<name>rscPermissions</name>

src/main/java/ru/simsonic/rscPermissions/BridgeForBukkitAPI.java

@@ -75,10 +75,18 @@ public class BridgeForBukkitAPI
 		if(rscp.permissionManager.isConsoleDebugging())
 		{
 			final StringBuilder sb = new StringBuilder(Settings.chatPrefix);
-			sb.append("[DEBUG] An API method was invoked from the path:\n");
+			sb.append("[DEBUG] An API method was invoked from the path:").append(System.lineSeparator());
 			for(StackTraceElement ste : Thread.currentThread().getStackTrace())
-				if(!ste.getClassName().equals(BridgeForBukkitAPI.class.getName()))
+			{
-					sb.append(ste.toString()).append(System.lineSeparator());
+				final String className = ste.getClassName();
+				if(!className.equals(BridgeForBukkitAPI.class.getName())
+					&& !className.equals(Thread.class.getName())
+					)
+					sb.append(Settings.chatPrefix).append("[DEBUG] ")
+						.append(className.startsWith(BukkitPluginMain.class.getPackage().getName()) ? "{_LG}" : "{_LS}")
+						.append(ste.toString())
+						.append(System.lineSeparator());
+			}
 			rscp.getServer().getConsoleSender().sendMessage(GenericChatCodes.processStringStatic(sb.toString()));
 		}
 	}

src/main/java/ru/simsonic/rscPermissions/Bukkit/BukkitPermissionManager.java

@@ -1,6 +1,7 @@
 package ru.simsonic.rscPermissions.Bukkit;
 import java.net.InetSocketAddress;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -122,9 +123,9 @@ public class BukkitPermissionManager extends RestartableThread
 						// Show debugging information
 						if(isDebugging(player))
 							player.sendMessage(GenericChatCodes.processStringStatic(Settings.chatPrefix
-								+ "[DEBUG] {_DS}Inheritances list: {_LS}" + result.groups.toString()
+								+ "[DEBUG] Inheritances list: {_LG}" + Arrays.toString(result.getDeorderedGroups())
-								+ "{_DS}; you have total {_LS}" + attachment.getPermissions().size()
+								+ "{_LS}; you have total {_LG}" + attachment.getPermissions().size()
-								+ "{_DS} permissions."));
+								+ "{_LS} permissions."));
 					}
 				});
 			}

src/main/java/ru/simsonic/rscPermissions/Bukkit/BukkitRegionProviders.java

@@ -3,6 +3,7 @@ import com.sk89q.worldguard.bukkit.WorldGuardPlugin;
 import com.sk89q.worldguard.protection.ApplicableRegionSet;
 import com.sk89q.worldguard.protection.managers.RegionManager;
 import com.sk89q.worldguard.protection.regions.ProtectedRegion;
+import java.io.Serializable;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -88,7 +89,8 @@ public final class BukkitRegionProviders
 				final ApplicableRegionSet appregs = rman.getApplicableRegions(location);
 				for(ProtectedRegion region : appregs)
 					playerRegions.add(region.getId());
-			} catch(RuntimeException ex) {
+			} catch(RuntimeException | IncompatibleClassChangeError ex) {
+				BukkitPluginMain.consoleLog.info(GenericChatCodes.processStringStatic("[rscp] " + Phrases.INTEGRATION_WG_OLD.toString()));
 			}
 		// Residence
 		if(residence != null && residence.isEnabled())

src/main/java/ru/simsonic/rscPermissions/Engine/InternalCache.java

@@ -304,7 +304,10 @@ public class InternalCache
 	}
 	public synchronized Set<String> getGroups()
 	{
-		return entities_g.keySet();
+		final HashSet<String> result = new HashSet<>(entities_g.size());
+		for(RowEntity row : entities_g.values())
+			result.add(row.entity);
+		return result;
 	}
 	public synchronized void clear()
 	{

src/main/java/ru/simsonic/rscPermissions/Engine/Phrases.java

@@ -20,6 +20,7 @@ public enum Phrases
 	INTEGRATION_V_N    ("integration.vault-no"),
 	INTEGRATION_WG_Y   ("integration.worldguard-yes"),
 	INTEGRATION_WG_N   ("integration.worldguard-no"),
+	INTEGRATION_WG_OLD ("integration.worldguard-old"),
 	INTEGRATION_R_Y    ("integration.residence-yes"),
 	INTEGRATION_R_N    ("integration.residence-no"),
 	DEBUG_ON           ("debug.enable"),

src/main/resources/languages/english.yml

@@ -10,6 +10,7 @@ integration:
   vault-no:       "{_LR}There is no Vault found. Vault is highly recommended to be installed on your server."
   worldguard-yes: "{_LG}WorldGuard was found and integrated."
   worldguard-no:  "{_YL}WorldGuard was not found."
+  worldguard-old: "{_LR}WorldGuard 5.9 or older is found, I need 6.0 or later. {_YL}Region support for WG is disabled."
   residence-yes:  "{_LG}Residence was found and integrated."
   residence-no:   "{_YL}Residence was not found."
 debug:

src/main/resources/languages/russian.yml

@@ -10,6 +10,7 @@ integration:
   vault-no:       "{_LR}Не удаётся найти плагин Vault. Рекомендуется его скорейшая установка."
   worldguard-yes: "{_LG}WorldGuard обнаружён и подключён."
   worldguard-no:  "{_YL}WorldGuard не обнаружен."
+  worldguard-old: "{_LR}Найден WorldGuard 5.9 или старше, но для работы требуется версия 6.0 или новее. {_YL}Поддержка регионов WG будет отключена."
   residence-yes:  "{_LG}Residence обнаружён и подключён."
   residence-no:   "{_YL}Residence не обнаружен."
 debug: