make creating new job as cron is blank

src/main/java/org/codelibs/fess/app/web/admin/scheduler/AdminSchedulerAction.java

@@ -125,6 +125,7 @@ public class AdminSchedulerAction extends FessAdminAction {
                         scheduledJobForm.jobLogging = Constants.ON;
                         scheduledJobForm.crawler = Constants.ON;
                         scheduledJobForm.available = Constants.ON;
+                        scheduledJobForm.cronExpression = null;
                         scheduledJobForm.name =
                                 ComponentUtil.getMessageManager().getMessage(LaRequestUtil.getRequest().getLocale(),
                                         "labels." + type + "_job_title", name);

src/main/java/org/codelibs/fess/app/web/admin/scheduler/CreateForm.java

@@ -45,7 +45,6 @@ public class CreateForm implements Serializable {
     @Size(max = 100)
     public String target;
 
-    @Required
     @Size(max = 100)
     @CronExpression
     public String cronExpression;

src/main/java/org/codelibs/fess/job/JobScheduler.java

@@ -120,17 +120,18 @@ public class JobScheduler {
         jobDataMap.put(Constants.JOB_EXECUTOR_TYPE, scriptType);
         final JobDetail jobDetail = newJob(jobClass).withIdentity(jobId).usingJobData(jobDataMap).build();
 
-        final Trigger trigger =
-                newTrigger().withIdentity(triggerId).withSchedule(cronSchedule(scheduledJob.getCronExpression())).startNow().build();
+        if (StringUtil.isNotBlank(scheduledJob.getCronExpression())) {
+            final Trigger trigger =
+                    newTrigger().withIdentity(triggerId).withSchedule(cronSchedule(scheduledJob.getCronExpression())).startNow().build();
 
-        try {
-            scheduler.scheduleJob(jobDetail, trigger);
-        } catch (final SchedulerException e) {
-            throw new ScheduledJobException("Failed to add Job: " + scheduledJob, e);
-        }
-
-        logger.info("Starting Job " + scheduledJob.getId() + ":" + scheduledJob.getName());
+            try {
+                scheduler.scheduleJob(jobDetail, trigger);
+            } catch (final SchedulerException e) {
+                throw new ScheduledJobException("Failed to add Job: " + scheduledJob, e);
+            }
 
+            logger.info("Starting Job " + scheduledJob.getId() + ":" + scheduledJob.getName());
+        }
     }
 
     public void unregister(final ScheduledJob scheduledJob) {