diff --git a/api/src/main/java/de/erethon/dungeonsxl/api/dungeon/CollectionGameRule.java b/api/src/main/java/de/erethon/dungeonsxl/api/dungeon/CollectionGameRule.java
index 01487866..7b51279b 100644
--- a/api/src/main/java/de/erethon/dungeonsxl/api/dungeon/CollectionGameRule.java
+++ b/api/src/main/java/de/erethon/dungeonsxl/api/dungeon/CollectionGameRule.java
@@ -16,6 +16,7 @@ package de.erethon.dungeonsxl.api.dungeon;
 
 import de.erethon.dungeonsxl.api.DungeonsAPI;
 import java.util.Collection;
+import org.apache.commons.lang.Validate;
 import org.bukkit.configuration.ConfigurationSection;
 
 /**
@@ -31,11 +32,12 @@ public class CollectionGameRule<T, V extends Collection<T>> extends GameRule<V>
 
     /**
      * @param key          the configuration key of the game rule
-     * @param defaultValue the default value that is used when nothing is set
+     * @param defaultValue the default value that is used when nothing is set; not null
      * @param copier       a method to copy the collection
      */
     public CollectionGameRule(String key, V defaultValue, Copier<V> copier) {
         super(null, key, defaultValue);
+        Validate.notNull(defaultValue, "defaultValue must not be null");
         this.copier = copier;
     }
 
diff --git a/api/src/main/java/de/erethon/dungeonsxl/api/dungeon/GameRule.java b/api/src/main/java/de/erethon/dungeonsxl/api/dungeon/GameRule.java
index f269fb9e..4d4f15c0 100644
--- a/api/src/main/java/de/erethon/dungeonsxl/api/dungeon/GameRule.java
+++ b/api/src/main/java/de/erethon/dungeonsxl/api/dungeon/GameRule.java
@@ -108,20 +108,20 @@ public class GameRule<V> {
      * A whitelist of breakable blocks. breakBlocks is supposed to be set to "true" if this should be used.
      */
     public static final GameRule<Map<ExItem, HashSet<ExItem>>> BREAK_WHITELIST
-            = new MapGameRule<>("breakWhitelist", null, ConfigReader.TOOL_BLOCK_MAP_READER, HashMap::new);
+            = new MapGameRule<>("breakWhitelist", new HashMap<>(), ConfigReader.TOOL_BLOCK_MAP_READER, HashMap::new);
     /**
      * A blacklist of block types players cannot interact with.
      */
     public static final GameRule<Map<ExItem, HashSet<ExItem>>> INTERACTION_BLACKLIST
-            = new MapGameRule<>("interactionBlacklist", null, ConfigReader.TOOL_BLOCK_MAP_READER, HashMap::new);
+            = new MapGameRule<>("interactionBlacklist", new HashMap<>(), ConfigReader.TOOL_BLOCK_MAP_READER, HashMap::new);
     /**
      * A list of all entity types that shall be protected from damage.
      */
-    public static final GameRule<Set<ExMob>> DAMAGE_PROTECTED_ENTITIES = new CollectionGameRule<>("damageProtectedEntities", null, ConfigReader.EX_MOB_SET_READER, HashSet::new);
+    public static final GameRule<Set<ExMob>> DAMAGE_PROTECTED_ENTITIES = new CollectionGameRule<>("damageProtectedEntities", new HashSet<>(), ConfigReader.EX_MOB_SET_READER, HashSet::new);
     /**
      * A list of all entity types that shall be protected from interaction.
      */
-    public static final GameRule<Set<ExMob>> INTERACTION_PROTECTED_ENTITIES = new CollectionGameRule<>("interactionProtectedEntities", null, ConfigReader.EX_MOB_SET_READER, HashSet::new);
+    public static final GameRule<Set<ExMob>> INTERACTION_PROTECTED_ENTITIES = new CollectionGameRule<>("interactionProtectedEntities", new HashSet<>(), ConfigReader.EX_MOB_SET_READER, HashSet::new);
     /**
      * If blocks may be placed.
      */
@@ -129,13 +129,13 @@ public class GameRule<V> {
     /**
      * A whitelist of placeable blocks. placeBlocks is supposed to be set to "true" if this should be used.
      */
-    public static final GameRule<Set<ExItem>> PLACE_WHITELIST = new CollectionGameRule<>("placeWhitelist", null, ConfigReader.EX_ITEM_SET_READER, HashSet::new);
+    public static final GameRule<Set<ExItem>> PLACE_WHITELIST = new CollectionGameRule<>("placeWhitelist", new HashSet<>(), ConfigReader.EX_ITEM_SET_READER, HashSet::new);
     /**
      * A set of blocks that do not fade.
      *
      * @see <a href="https://hub.spigotmc.org/javadocs/spigot/org/bukkit/event/block/BlockFadeEvent.html">org.bukkit.event.block.BlockFadeEvent</a>
      */
-    public static final GameRule<Set<ExItem>> BLOCK_FADE_DISABLED = new CollectionGameRule<>("blockFadeDisabled", null, ConfigReader.EX_ITEM_SET_READER, HashSet::new);
+    public static final GameRule<Set<ExItem>> BLOCK_FADE_DISABLED = new CollectionGameRule<>("blockFadeDisabled", new HashSet<>(), ConfigReader.EX_ITEM_SET_READER, HashSet::new);
     /**
      * This does what the doFireTick Vanilla game rule does.
      */
@@ -242,11 +242,11 @@ public class GameRule<V> {
     /**
      * One of these Dungeons must be finished ("any" for any dungeon).
      */
-    public static final GameRule<List<String>> MUST_FINISH_ONE = new CollectionGameRule<>("mustFinishOne", null, ArrayList::new);
+    public static final GameRule<List<String>> MUST_FINISH_ONE = new CollectionGameRule<>("mustFinishOne", new ArrayList<>(), ArrayList::new);
     /**
      * All of these Dungeons must be finished. If you do not want any, leave this empty.
      */
-    public static final GameRule<List<String>> MUST_FINISH_ALL = new CollectionGameRule<>("mustFinishAll", null, ArrayList::new);
+    public static final GameRule<List<String>> MUST_FINISH_ALL = new CollectionGameRule<>("mustFinishAll", new ArrayList<>(), ArrayList::new);
     /**
      * This can be used to give rewards. The default implementation does not do this at the moment.
      */
diff --git a/api/src/main/java/de/erethon/dungeonsxl/api/dungeon/MapGameRule.java b/api/src/main/java/de/erethon/dungeonsxl/api/dungeon/MapGameRule.java
index f1f793a3..a49d940b 100644
--- a/api/src/main/java/de/erethon/dungeonsxl/api/dungeon/MapGameRule.java
+++ b/api/src/main/java/de/erethon/dungeonsxl/api/dungeon/MapGameRule.java
@@ -16,6 +16,7 @@ package de.erethon.dungeonsxl.api.dungeon;
 
 import de.erethon.dungeonsxl.api.DungeonsAPI;
 import java.util.Map;
+import org.apache.commons.lang.Validate;
 import org.bukkit.configuration.ConfigurationSection;
 
 /**
@@ -32,12 +33,13 @@ public class MapGameRule<TK, TV, V extends Map<TK, TV>> extends GameRule<V> {
 
     /**
      * @param key          the configuration key of the game rule
-     * @param defaultValue the default value that is used when nothing is set
+     * @param defaultValue the default value that is used when nothing is set; not null
      * @param reader       a functional interface that loads the value from config
      * @param copier       a method to copy the map
      */
     public MapGameRule(String key, V defaultValue, ConfigReader<V> reader, Copier<V> copier) {
         super(null, key, defaultValue, reader);
+        Validate.notNull(defaultValue, "defaultValue must not be null");
         this.copier = copier;
     }
 
diff --git a/core/src/main/java/de/erethon/dungeonsxl/player/DGlobalPlayer.java b/core/src/main/java/de/erethon/dungeonsxl/player/DGlobalPlayer.java
index 616da56b..8e76f345 100644
--- a/core/src/main/java/de/erethon/dungeonsxl/player/DGlobalPlayer.java
+++ b/core/src/main/java/de/erethon/dungeonsxl/player/DGlobalPlayer.java
@@ -307,9 +307,9 @@ public class DGlobalPlayer implements GlobalPlayer {
             msgs.forEach(msg -> MessageUtil.sendMessage(player, msg));
         }
 
-        if (rules.getState(GameRule.MUST_FINISH_ALL) != null) {
+        if (!rules.getState(GameRule.MUST_FINISH_ALL).isEmpty()) {
             List<String> finished = new ArrayList<>(rules.getState(GameRule.MUST_FINISH_ALL));
-            if (rules.getState(GameRule.MUST_FINISH_ONE) != null) {
+            if (!rules.getState(GameRule.MUST_FINISH_ONE).isEmpty()) {
                 finished.addAll(rules.getState(GameRule.MUST_FINISH_ONE));
             }
 
@@ -358,7 +358,6 @@ public class DGlobalPlayer implements GlobalPlayer {
                 if (numOfNeeded < rules.getState(GameRule.MUST_FINISH_ALL).size() || !doneTheOne) {
                     fulfilled = false;
                 }
-
             }
         }
 
diff --git a/core/src/main/java/de/erethon/dungeonsxl/world/DGameWorld.java b/core/src/main/java/de/erethon/dungeonsxl/world/DGameWorld.java
index 5f471d72..ffd244a5 100644
--- a/core/src/main/java/de/erethon/dungeonsxl/world/DGameWorld.java
+++ b/core/src/main/java/de/erethon/dungeonsxl/world/DGameWorld.java
@@ -602,7 +602,7 @@ public class DGameWorld extends DInstanceWorld implements GameWorld {
         }
 
         Set<ExItem> whitelist = getRules().getState(GameRule.PLACE_WHITELIST);
-        if (whitelist == null || whitelist.contains(VanillaItem.get(block.getType()))) {
+        if (whitelist.isEmpty() || whitelist.contains(VanillaItem.get(block.getType()))) {
             placedBlocks.add(block);
             return false;
         }
diff --git a/core/src/main/java/de/erethon/dungeonsxl/world/DWorldListener.java b/core/src/main/java/de/erethon/dungeonsxl/world/DWorldListener.java
index 4ec044d3..18706fa5 100644
--- a/core/src/main/java/de/erethon/dungeonsxl/world/DWorldListener.java
+++ b/core/src/main/java/de/erethon/dungeonsxl/world/DWorldListener.java
@@ -123,7 +123,7 @@ public class DWorldListener implements Listener {
         }
 
         Map<ExItem, HashSet<ExItem>> blacklist = gameWorld.getDungeon().getRules().getState(GameRule.INTERACTION_BLACKLIST);
-        if (blacklist == null) {
+        if (blacklist.isEmpty()) {
             return;
         }
 
@@ -254,7 +254,7 @@ public class DWorldListener implements Listener {
         }
 
         Set<ExItem> blockFadeDisabled = gameWorld.getGame().getRules().getState(GameRule.BLOCK_FADE_DISABLED);
-        if (blockFadeDisabled == null) {
+        if (blockFadeDisabled.isEmpty()) {
             return;
         }
         if (gameWorld.getGame() != null && blockFadeDisabled.contains(VanillaItem.get(event.getBlock().getType()))) {