validate data is not empty

task-executor-kit/task-executor-core/src/main/java/com/mushiny/task/executor/core/TaskExecutor.java

@@ -69,6 +69,7 @@ public class TaskExecutor<T, U, R> {
         TaskDefinition<T, U, R> t = this.task;
         Collection<T> data = t.getData();
         if (null == data || data.isEmpty()) {
+            log.warn("data is empty");
             return false;
         }
         countDownLatch = new CountDownLatch(data.size());