diff --git a/x2-data-explorer/src/main/resources/defaultStateObjSummary.groovy b/x2-data-explorer/src/main/resources/defaultStateObjSummary.groovy
index cfd8fcd..9a2c8b3 100644
--- a/x2-data-explorer/src/main/resources/defaultStateObjSummary.groovy
+++ b/x2-data-explorer/src/main/resources/defaultStateObjSummary.groovy
@@ -14,11 +14,10 @@ if (gso.ApplyEffectParameters) {
 	} else {
 		source = gso.ApplyEffectParameters.EffectRef.LookupType.value.original
 	}
-	return source +
-			' by ' +
-			gso.ApplyEffectParameters.SourceStateObjectRef.ObjectID.value +
-			' on ' +
-			gso.ApplyEffectParameters.TargetStateObjectRef.ObjectID.value
+	if (gso.ApplyEffectParameters.SourceStateObjectRef) { // effects applied by XCGSC_UpdateWorldEffects do not have a source
+		source += ' by ' + gso.ApplyEffectParameters.SourceStateObjectRef.ObjectID.value
+	}
+	return source + ' on ' + gso.ApplyEffectParameters.TargetStateObjectRef.ObjectID.value
 }
 
 // XComGameState_Unit