diff --git a/OpenRA.Mods.RA/AI/HackyAI.cs b/OpenRA.Mods.RA/AI/HackyAI.cs
index a4e92f2c9e..4d46d71a39 100644
--- a/OpenRA.Mods.RA/AI/HackyAI.cs
+++ b/OpenRA.Mods.RA/AI/HackyAI.cs
@@ -483,7 +483,7 @@ namespace OpenRA.Mods.RA.AI
 
 		void CleanSquads()
 		{
-			squads.RemoveAll(s => s.IsEmpty);
+			squads.RemoveAll(s => !s.IsValid);
 			foreach (var s in squads)
 				s.units.RemoveAll(a => a.Destroyed || a.IsDead());
 		}
@@ -647,7 +647,7 @@ namespace OpenRA.Mods.RA.AI
 			if (!protectSq.TargetIsValid)
 				protectSq.Target = attacker;
 
-			if (protectSq.IsEmpty)
+			if (!protectSq.IsValid)
 			{
 				var ownUnits = world.FindActorsInCircle(baseCenter.CenterPosition, WRange.FromCells(15))
 					.Where(unit => unit.Owner == p && !unit.HasTrait<Building>()
diff --git a/OpenRA.Mods.RA/AI/Squad.cs b/OpenRA.Mods.RA/AI/Squad.cs
index ab79b7bf99..84da2e26d0 100644
--- a/OpenRA.Mods.RA/AI/Squad.cs
+++ b/OpenRA.Mods.RA/AI/Squad.cs
@@ -61,14 +61,11 @@ namespace OpenRA.Mods.RA.AI
 
 		public void Update()
 		{
-			if (IsEmpty) return;
-			fsm.Update(this);
+			if (IsValid)
+				fsm.Update(this);
 		}
 
-		public bool IsEmpty
-		{
-			get { return !units.Any(); }
-		}
+		public bool IsValid { get { return units.Any(); } }
 
 		public Actor Target
 		{
diff --git a/OpenRA.Mods.RA/AI/States/AirStates.cs b/OpenRA.Mods.RA/AI/States/AirStates.cs
index fac3ea5c07..3cfe6b70e0 100644
--- a/OpenRA.Mods.RA/AI/States/AirStates.cs
+++ b/OpenRA.Mods.RA/AI/States/AirStates.cs
@@ -151,7 +151,8 @@ namespace OpenRA.Mods.RA.AI
 
 		public void Tick(Squad owner)
 		{
-			if (owner.IsEmpty) return;
+			if (!owner.IsValid)
+				return;
 
 			if (MayBeFlee(owner))
 			{
@@ -178,7 +179,8 @@ namespace OpenRA.Mods.RA.AI
 
 		public void Tick(Squad owner)
 		{
-			if (owner.IsEmpty) return;
+			if (!owner.IsValid)
+				return;
 
 			if (!owner.TargetIsValid)
 			{
@@ -229,7 +231,8 @@ namespace OpenRA.Mods.RA.AI
 
 		public void Tick(Squad owner)
 		{
-			if (owner.IsEmpty) return;
+			if (!owner.IsValid)
+				return;
 
 			foreach (var a in owner.units)
 			{
diff --git a/OpenRA.Mods.RA/AI/States/GroundStates.cs b/OpenRA.Mods.RA/AI/States/GroundStates.cs
index 1799603bab..28574ff43d 100644
--- a/OpenRA.Mods.RA/AI/States/GroundStates.cs
+++ b/OpenRA.Mods.RA/AI/States/GroundStates.cs
@@ -35,7 +35,9 @@ namespace OpenRA.Mods.RA.AI
 
 		public void Tick(Squad owner)
 		{
-			if (owner.IsEmpty) return;
+			if (!owner.IsValid)
+				return;
+
 			if (!owner.TargetIsValid)
 			{
 				var t = owner.bot.FindClosestEnemy(owner.units.FirstOrDefault().CenterPosition);
@@ -71,7 +73,8 @@ namespace OpenRA.Mods.RA.AI
 
 		public void Tick(Squad owner)
 		{
-			if (owner.IsEmpty) return;
+			if (!owner.IsValid)
+				return;
 
 			if (!owner.TargetIsValid)
 			{
@@ -128,7 +131,8 @@ namespace OpenRA.Mods.RA.AI
 
 		public void Tick(Squad owner)
 		{
-			if (owner.IsEmpty) return;
+			if (!owner.IsValid)
+				return;
 
 			if (!owner.TargetIsValid)
 			{
@@ -161,7 +165,8 @@ namespace OpenRA.Mods.RA.AI
 
 		public void Tick(Squad owner)
 		{
-			if (owner.IsEmpty) return;
+			if (!owner.IsValid)
+				return;
 
 			GoToRandomOwnBuilding(owner);
 			owner.fsm.ChangeState(owner, new GroundUnitsIdleState(), true);
diff --git a/OpenRA.Mods.RA/AI/States/ProtectionStates.cs b/OpenRA.Mods.RA/AI/States/ProtectionStates.cs
index e365116fb8..06e954ab87 100644
--- a/OpenRA.Mods.RA/AI/States/ProtectionStates.cs
+++ b/OpenRA.Mods.RA/AI/States/ProtectionStates.cs
@@ -27,7 +27,9 @@ namespace OpenRA.Mods.RA.AI
 
 		public void Tick(Squad owner)
 		{
-			if (owner.IsEmpty) return;
+			if (!owner.IsValid)
+				return;
+
 			if (!owner.TargetIsValid)
 			{
 				var circaPostion = AverageUnitsPosition(owner.units);
@@ -53,7 +55,8 @@ namespace OpenRA.Mods.RA.AI
 
 		public void Tick(Squad owner)
 		{
-			if (owner.IsEmpty) return;
+			if (!owner.IsValid)
+				return;
 
 			GoToRandomOwnBuilding(owner);
 			owner.fsm.ChangeState(owner, new UnitsForProtectionIdleState(), true);
diff --git a/OpenRA.Mods.RA/AI/States/StateBase.cs b/OpenRA.Mods.RA/AI/States/StateBase.cs
index 78d63e82e6..eee78e7515 100644
--- a/OpenRA.Mods.RA/AI/States/StateBase.cs
+++ b/OpenRA.Mods.RA/AI/States/StateBase.cs
@@ -28,7 +28,9 @@ namespace OpenRA.Mods.RA.AI
 
 		protected virtual bool MayBeFlee(Squad owner, Func<List<Actor>, bool> flee)
 		{
-			if (owner.IsEmpty) return false;
+			if (!owner.IsValid)
+				return false;
+
 			var u = owner.units.Random(owner.random);
 
 			var units = owner.world.FindActorsInCircle(u.CenterPosition, WRange.FromCells(dangerRadius)).ToList();