From c286eeaa16c8182e3b2dd94fa0dfde087314e51d Mon Sep 17 00:00:00 2001
From: JoePfeiffer <joseph@pfeifferfamily.net>
Date: Fri, 20 Jan 2023 17:45:47 -0700
Subject: [PATCH] check for children before taking child in geometry check.

---
 .../net/sf/openrocket/aerodynamics/BarrowmanCalculator.java    | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/core/src/net/sf/openrocket/aerodynamics/BarrowmanCalculator.java b/core/src/net/sf/openrocket/aerodynamics/BarrowmanCalculator.java
index 4dd02050d..129f4f17c 100644
--- a/core/src/net/sf/openrocket/aerodynamics/BarrowmanCalculator.java
+++ b/core/src/net/sf/openrocket/aerodynamics/BarrowmanCalculator.java
@@ -291,7 +291,8 @@ public class BarrowmanCalculator extends AbstractAerodynamicCalculator {
 
 		SymmetricComponent prevComp = null;		
 		if ((treeRoot instanceof ComponentAssembly) &&
-			(!(treeRoot instanceof Rocket))) {
+			(!(treeRoot instanceof Rocket)) &&
+			(treeRoot.getChildCount() > 0)) {
 			prevComp = ((SymmetricComponent) (treeRoot.getChild(0))).getPreviousSymmetricComponent();
 		}