Fixed a bunch of NPE and other possible exceptions.

Mage.Common/src/mage/view/GameView.java

@@ -95,8 +95,8 @@ public class GameView implements Serializable {
         }
         for (StackObject stackObject: state.getStack()) {
             if (stackObject instanceof StackAbility) {
-                // Stack Ability
-                MageObject object = game.getObject(stackObject.getSourceId());
+                // Stack Ability                
+                MageObject object = ((StackAbility)stackObject).getSourceObject(game);
                 Card card = game.getCard(stackObject.getSourceId());
                 if (card != null) {
                     if (object != null) {

Mage.Server/src/main/java/mage/server/TableController.java

@@ -558,7 +558,6 @@ public class TableController {
                 if (!match.getPlayer(entry.getValue()).hasQuit()) {
                     User user = UserManager.getInstance().getUser(entry.getKey());
                     if (user != null) {
-                        Player player = match.getPlayer(entry.getValue()).getPlayer();
                         user.ccGameStarted(match.getGame().getId(), entry.getValue());
                         
                         if (creator == null) {

Mage.Sets/src/mage/sets/dragonsoftarkir/DragonlordsPrerogative.java

@@ -31,6 +31,7 @@ import java.util.UUID;
 import mage.abilities.Ability;
 import mage.abilities.common.SimpleStaticAbility;
 import mage.abilities.condition.Condition;
+import mage.abilities.costs.Cost;
 import mage.abilities.costs.common.RevealTargetFromHandCost;
 import mage.abilities.decorator.ConditionalContinuousRuleModifyingEffect;
 import mage.abilities.effects.ContinuousRuleModifyingEffect;
@@ -114,9 +115,11 @@ class DragonlordsPrerogativeCondition implements Condition {
         boolean applies = false;
         Spell spell = game.getStack().getSpell(source.getSourceId());
         if (spell != null) {
-            RevealTargetFromHandCost cost = (RevealTargetFromHandCost) spell.getSpellAbility().getCosts().get(0);
-            if (cost != null) {
-                applies = !cost.getTargets().isEmpty();
+            for(Cost cost: spell.getSpellAbility().getCosts()) {
+                if (cost instanceof RevealTargetFromHandCost) {
+                    applies = !((RevealTargetFromHandCost)cost).getTargets().isEmpty();
+                    break;
+                }
             }
         }
         if (!applies) {

Mage.Sets/src/mage/sets/dragonsoftarkir/LivingLore.java

@@ -196,9 +196,11 @@ class LivingLoreSacrificeEffect extends OneShotEffect {
                     if (exileId != null) {
                         ExileZone exileZone = game.getExile().getExileZone(exileId);
                         Card exiledCard = null;
-                        for (Card card :exileZone.getCards(game)) {
-                            exiledCard = card;
-                            break;
+                        if (exileZone != null) {
+                            for (Card card :exileZone.getCards(game)) {
+                                exiledCard = card;
+                                break;
+                            }
                         }
                         if (exiledCard != null) {
                             if (exiledCard.getSpellAbility().canChooseTarget(game)) {

Mage.Sets/src/mage/sets/mirrodin/AuriokSteelshaper.java

@@ -38,7 +38,6 @@ import mage.abilities.effects.common.cost.CostModificationEffectImpl;
 import mage.abilities.keyword.EquipAbility;
 import mage.cards.CardImpl;
 import mage.constants.*;
-import mage.filter.FilterAbility;
 import mage.filter.common.FilterCreaturePermanent;
 import mage.filter.predicate.Predicates;
 import mage.filter.predicate.mageobject.SubtypePredicate;

Mage.Tests/src/test/java/org/mage/test/cards/abilities/keywords/BestowTest.java

@@ -278,4 +278,34 @@ public class BestowTest extends CardTestPlayerBase {
         assertPowerToughness(playerA, "Silvercoat Lion", 3,3);
 
     }
+    
+  /**
+     * 
+     * 
+     * 
+     */
+    @Test
+    public void bestowMogissWarhound() {
+        addCard(Zone.BATTLEFIELD, playerA, "Mountain", 3);
+        // Enchantment Creature — Hound
+        // 2/2
+        // Bestow 2R (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)
+        // Mogis's Warhound attacks each turn if able.
+        // Enchanted creature gets +2/+2 and attacks each turn if able.
+        addCard(Zone.HAND, playerA, "Mogis's Warhound");
+        addCard(Zone.BATTLEFIELD, playerA, "Silvercoat Lion");
+
+        castSpell(1, PhaseStep.PRECOMBAT_MAIN, playerA, "Mogis's Warhound using bestow", "Silvercoat Lion");
+
+        setStopAt(3, PhaseStep.BEGIN_COMBAT);
+        execute();
+
+        //
+        assertHandCount(playerA, "Mogis's Warhound", 0);
+
+        // because cast with bestow, Boon Satyr may not be tapped
+        assertPermanentCount(playerA, "Silvercoat Lion", 1);
+        assertPowerToughness(playerA, "Silvercoat Lion", 4,4);
+
+    }    
 }

Mage/src/mage/abilities/AbilitiesImpl.java

@@ -31,6 +31,7 @@ package mage.abilities;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.Iterator;
 import java.util.List;
 import java.util.UUID;
 import mage.abilities.common.ZoneChangeTriggeredAbility;
@@ -249,7 +250,8 @@ public class AbilitiesImpl<T extends Ability> extends ArrayList<T> implements Ab
 
     @Override
     public boolean contains(T ability) {
-        for (T test: this) {
+        for (Iterator<T> iterator = this.iterator(); iterator.hasNext();) { // simple loop can cause java.util.ConcurrentModificationException
+             T test = iterator.next();
             // Checking also by getRule() without other restrictions is a problem when a triggered ability will be copied to a permanent that had the same ability
             // already before the copy. Because then it keeps the triggered ability twice and it triggers twice.
             // e.g. 2 Biovisonary and one enchanted with Infinite Reflection

Mage/src/mage/abilities/effects/ContinuousEffectsList.java

@@ -173,7 +173,9 @@ public class ContinuousEffectsList<T extends ContinuousEffect> extends ArrayList
 
     public void removeEffects(UUID effectIdToRemove, Set<Ability> abilitiesToRemove) {
         HashSet<Ability> abilities = effectAbilityMap.get(effectIdToRemove);
-        abilities.removeAll(abilitiesToRemove);
+        if (abilitiesToRemove != null) {
+            abilities.removeAll(abilitiesToRemove);
+        }
         if (abilities.isEmpty()) {
             for (Iterator<T> iterator = this.iterator(); iterator.hasNext();) {
                 ContinuousEffect effect = iterator.next();

Mage/src/mage/abilities/effects/common/ReturnToBattlefieldUnderYourControlTargetEffect.java

@@ -29,12 +29,12 @@
 package mage.abilities.effects.common;
 
 import java.util.UUID;
-import mage.MageObject;
 import mage.constants.Outcome;
 import mage.constants.Zone;
 import mage.abilities.Ability;
 import mage.abilities.effects.OneShotEffect;
 import mage.cards.Card;
+import mage.game.ExileZone;
 import mage.game.Game;
 import mage.players.Player;
 import mage.util.CardUtil;
@@ -79,7 +79,10 @@ public class ReturnToBattlefieldUnderYourControlTargetEffect extends OneShotEffe
             if (fromExileZone) {
                 UUID exilZoneId = CardUtil.getExileZoneId(game, source.getSourceId(), source.getSourceObjectZoneChangeCounter());
                 if (exilZoneId != null) {
-                card = game.getExile().getExileZone(exilZoneId).get(getTargetPointer().getFirst(game, source), game);
+                    ExileZone exileZone = game.getExile().getExileZone(exilZoneId);
+                    if (exileZone != null && getTargetPointer().getFirst(game, source) != null) {
+                        card = exileZone.get(getTargetPointer().getFirst(game, source), game);
+                    }                
                 }
             } else {
                 card = game.getCard(targetPointer.getFirst(game, source));

Mage/src/mage/abilities/effects/common/continuous/BoostSourceEffect.java

@@ -39,6 +39,7 @@ import mage.constants.Outcome;
 import mage.constants.SubLayer;
 import mage.game.Game;
 import mage.game.permanent.Permanent;
+import org.apache.log4j.Logger;
 
 /**
  *
@@ -87,7 +88,11 @@ public class BoostSourceEffect extends ContinuousEffectImpl implements SourceEff
     public void init(Ability source, Game game) {
         super.init(source, game);
         if (affectedObjectsSet) {
-            affectedObjectList.add(new MageObjectReference(source.getSourceId(), game));
+            try {
+                affectedObjectList.add(new MageObjectReference(source.getSourceId(), game));
+            } catch (IllegalArgumentException ex) {
+                Logger.getLogger(BoostSourceEffect.class).error("Could not get sourceId reference: " + source.getRule());
+            }
         }
         if (lockedIn) {
             power = new StaticValue(power.calculate(game, source, this));

Mage/src/mage/players/PlayerImpl.java

@@ -709,8 +709,10 @@ public abstract class PlayerImpl implements Player, Serializable {
             choose(Outcome.Discard, target, source == null ? null : source.getSourceId(), game);
             for (UUID cardId : target.getTargets()) {
                 Card card = this.getHand().get(cardId, game);
-                discardedCards.add(card);
-                discard(card, source, game);
+                if (card != null) { // can happen if user is removed (session expires)
+                    discardedCards.add(card);
+                    discard(card, source, game);
+                }
             }
         }
         return discardedCards;

Mage/src/mage/util/CardUtil.java

@@ -208,7 +208,7 @@ public class CardUtil {
      * @param ability
      * @param reduceCount
      */
-    public static void adjustAbilityCost(Ability ability, int reduceCount) {
+    private static void adjustAbilityCost(Ability ability, int reduceCount) {
         ManaCosts<ManaCost> adjustedCost = adjustCost(ability.getManaCostsToPay(), reduceCount);
         ability.getManaCostsToPay().clear();
         ability.getManaCostsToPay().addAll(adjustedCost);