[KYUUBI #2668][FOLLOWUP] Remove unused Option because the collection is never null

### _Why are the changes needed?_

This is a followup of #2668, refactor the code.

### _How was this patch tested?_
- [ ] Add some test cases that check the changes thoroughly including negative and positive cases if possible

- [ ] Add screenshots for manual tests if appropriate

- [ ] [Run test](https://kyuubi.apache.org/docs/latest/develop_tools/testing.html#running-tests) locally before make a pull request

Closes #2688 from turboFei/dto_batch_request_follow.

Closes #2668

1c07c75 [Fei Wang] Follow up for dto classes

Authored-by: Fei Wang <fwang12@ebay.com>
Signed-off-by: Fei Wang <fwang12@ebay.com>

Author: turboFei

kyuubi-server/src/main/scala/org/apache/kyuubi/server/api/v1/SessionsResource.scala

@@ -150,7 +150,7 @@ private[v1] class SessionsResource extends ApiRequestContext with Logging {
       userName,
       request.getPassword,
       ipAddress,
-      Option(request.getConfigs.asScala.toMap).getOrElse(Map.empty[String, String]))
+      request.getConfigs.asScala.toMap)
     new SessionHandle(
       handle.identifier.publicId,
       handle.identifier.secretId,

kyuubi-server/src/main/scala/org/apache/kyuubi/session/KyuubiBatchSessionImpl.scala

@@ -42,8 +42,7 @@ class KyuubiBatchSessionImpl(
 
   // TODO: Support batch conf advisor
   override val normalizedConf: Map[String, String] =
-    sessionManager.validateBatchConf(Option(batchRequest.getConf.asScala.toMap)
-      .getOrElse(Map.empty))
+    sessionManager.validateBatchConf(batchRequest.getConf.asScala.toMap)
 
   batchRequest.setConf(normalizedConf.asJava)