fixed a serious bug that sneaked in because I trust too much the refactoring tools that this time failed miserably

Svelto.ECS/DataStructures/TypeSafeFasterListForECS.cs

@@ -1,7 +1,7 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
-using DesignByContract;
+using DBC;
 using Svelto.DataStructures;
 
 namespace Svelto.ECS.Internal

Svelto.ECS/EnginesRootEntities.cs

@@ -1,6 +1,6 @@
 using System;
 using System.Collections.Generic;
-using DesignByContract;
+using DBC;
 using Svelto.DataStructures;
 using Svelto.ECS.Internal;
 

Svelto.ECS/EntityDescriptor.cs

@@ -1,5 +1,5 @@
 using System;
-using DesignByContract;
+using DBC;
 using Svelto.DataStructures;
 using Svelto.ECS.Internal;
 

Svelto.ECS/MultiEntityViewsEngine.cs

@@ -29,9 +29,8 @@ namespace Svelto.ECS
 
         public override void Add(IEntityView entityView)
         {
-            var castedEntityView = (U) entityView;
-            if (castedEntityView != null)
-                Add(castedEntityView);
+            if (entityView is U)
+                Add((U) entityView);
             else
                 base.Add(entityView);
         }
@@ -53,18 +52,16 @@ namespace Svelto.ECS
 
         public override void Add(IEntityView entityView)
         {
-            var castedEntityView = (V) entityView;
-            if (castedEntityView != null)
-                Add(castedEntityView);
+            if (entityView is V)
+                Add((V) entityView);
             else
                 base.Add(entityView);
         }
 
         public override void Remove(IEntityView entityView)
         {
-            var castedEntityView = (V) entityView;
-            if (castedEntityView != null)
-                Remove(castedEntityView);
+            if (entityView is V)
+                Remove((V) entityView);
             else
                 base.Remove(entityView);
         }
@@ -83,18 +80,16 @@ namespace Svelto.ECS
 
         public override void Add(IEntityView entityView)
         {
-            var castedEntityView = (W) entityView;
-            if (castedEntityView != null)
-                Add(castedEntityView);
+            if (entityView is W)
+                Add((W) entityView);
             else
                 base.Add(entityView);
         }
 
         public override void Remove(IEntityView entityView)
         {
-            var castedEntityView = (W) entityView;
-            if (castedEntityView != null)
-                Remove(castedEntityView);
+            if (entityView is W)
+                Remove((W) entityView);
             else
                 base.Remove(entityView);
         }

Svelto.ECS/Sequencer.cs

@@ -42,7 +42,7 @@ namespace Svelto.ECS
 
         public void Next<T>(IEngine engine, ref T param)
         {
-            Next<T>(engine, ref param, Condition.Always);
+            Next(engine, ref param, Condition.Always);
         }
 
         public void Next<T>(IEngine engine, ref T param, int condition)