Throw a better error than 'null' when someone removes all groups from a

yml.

EssentialsGroupManager/src/Changelog.txt

@@ -187,3 +187,4 @@ v 2.0:
 	- Only output a Data update message if something has changed.
 	- Fix loading users with only numerals in their names to be seen as strings.
 	- Ignore any sub folders in the Worlds folder which start with a period (fix for storing data in svn respoitories).
+	- Throw a better error than 'null' when someone removes all groups from a yml.

EssentialsGroupManager/src/org/anjocaido/groupmanager/dataholder/WorldDataHolder.java

@@ -509,6 +509,10 @@ public class WorldDataHolder {
 			throw new IllegalArgumentException("Your " + groupsFile.getPath() + " file is invalid. See console for details.", ex);
 		}
 		
+		if (allGroupsNode == null) {
+			throw new IllegalArgumentException("You have no groups in " + groupsFile.getPath() + ".");
+		}
+
 		Iterator<String> groupItr = allGroupsNode.keySet().iterator();
 		String groupKey;
 		Integer groupCount = 0;