Disable SerializationFeature.FAIL_ON_EMPTY_BEANS in dataMapper (#22)

Author: PetrHeinz

src/main/java/com/logtail/logback/LogtailAppender.java

@@ -9,6 +9,7 @@
 import com.fasterxml.jackson.databind.Module;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.PropertyNamingStrategies;
+import com.fasterxml.jackson.databind.SerializationFeature;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -75,7 +76,8 @@ public LogtailAppender() {
 
         dataMapper = new ObjectMapper()
                 .setSerializationInclusion(JsonInclude.Include.NON_NULL)
-                .setPropertyNamingStrategy(PropertyNamingStrategies.UPPER_CAMEL_CASE);
+                .setPropertyNamingStrategy(PropertyNamingStrategies.UPPER_CAMEL_CASE)
+                .disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);
 
         scheduledExecutorService = Executors.newSingleThreadScheduledExecutor(threadFactory);
         scheduledFuture = scheduledExecutorService.scheduleWithFixedDelay(new LogtailSender(), batchInterval, batchInterval, TimeUnit.MILLISECONDS);