diff --git a/Core/BehaviourTree.cs b/Core/BehaviourTree.cs
index 0bd004b..af97b67 100644
--- a/Core/BehaviourTree.cs
+++ b/Core/BehaviourTree.cs
@@ -421,6 +421,15 @@ void AddBlackboardAsset()
       }
     }
 
+    public void OnValidate()
+    {
+      var hasNullable = allNodes.Any(node => node == null);
+      if (hasNullable)
+      {
+        allNodes = allNodes.Where(node => node != null).ToArray();
+      }
+    }
+
     [HideInInspector]
     public Vector2 panPosition = Vector2.zero;
 
diff --git a/Core/Composite.cs b/Core/Composite.cs
index 18d3355..fd98813 100644
--- a/Core/Composite.cs
+++ b/Core/Composite.cs
@@ -1,4 +1,6 @@
 
+using System.Collections.Generic;
+using System.Linq;
 using UnityEngine;
 
 namespace Bonsai.Core
@@ -100,5 +102,16 @@ public sealed override int MaxChildCount()
       return int.MaxValue;
     }
 
+#if UNITY_EDITOR
+
+    private void OnValidate()
+    {
+      var hasNullable = children.Any(child => child == null);
+      if (hasNullable)
+      {
+        children = children.Where(child => child != null).ToArray();
+      }
+    }
+#endif
   }
 }
\ No newline at end of file