diff --git a/org.hl7.fhir.validation/src/main/java/org/hl7/fhir/validation/special/TxTester.java b/org.hl7.fhir.validation/src/main/java/org/hl7/fhir/validation/special/TxTester.java
index 89519f1db..25b57825f 100644
--- a/org.hl7.fhir.validation/src/main/java/org/hl7/fhir/validation/special/TxTester.java
+++ b/org.hl7.fhir.validation/src/main/java/org/hl7/fhir/validation/special/TxTester.java
@@ -167,7 +167,9 @@ public class TxTester {
 
   private boolean runTest(JsonObject test, TerminologyClient tx, List<Resource> setup, String filter, JsonArray output) { 
     JsonObject outputT = new JsonObject();
-    output.add(outputT);
+    if (output != null) {
+      output.add(outputT);
+    }
     outputT.add("name", test.asString("name"));
     if (Utilities.noString(filter) || filter.equals("*") || test.asString("name").contains(filter)) {
       System.out.print("  Test "+test.asString("name")+": ");