diff --git a/Editor/ClusterViewer.cs b/Editor/ClusterViewer.cs
index 565fdc5..86ae2a4 100644
--- a/Editor/ClusterViewer.cs
+++ b/Editor/ClusterViewer.cs
@@ -503,6 +503,9 @@ namespace NanoBrain {
             }
 
             protected void DrawOutputs(Vector2 parentPos, float size) {
+                if (this.currentCluster == null)
+                    return;
+                    
                 // Determine the maximum value in this layer
                 // This is used to 'scale' the output value colors of the nuclei
                 float maxValue = 0;