Change the visibility of the reportParser field:

src/main/java/net/masterthought/cucumber/ReportBuilder.java

@@ -53,7 +53,7 @@ public class ReportBuilder {
     private static final ObjectMapper mapper = new ObjectMapper();
 
     private ReportResult reportResult;
-    private final ReportParser reportParser;
+    protected ReportParser reportParser;
 
     private Configuration configuration;
     private List<String> jsonFiles;