Refactor: Use pthread_exit(nullptr) instead of pthread_exit(NULL) for type safety.

Author: gberkes

examples/reading_logs_via_rule_message/reading_logs_via_rule_message.h

@@ -102,7 +102,7 @@ struct data_ms {
         delete modsecTransaction;
     }
 
-    pthread_exit(NULL);
+    pthread_exit(nullptr);
 }