Do Not Invoke emailNotification without LAVA Jobs

Invoking emailNotification when there is no LAVA job submitted
would cause an error, because output is a null value.
This function should only be invoked
when there are LAVA jobs submitted.

Change-Id: Ic79673355eef8796ad62dcf517fe3b4003aa550a
Signed-off-by: Xinyu Zhang <xinyu.zhang@arm.com>
diff --git a/jenkins/ci.jpl b/jenkins/ci.jpl
index acb2d96..bb5f73f 100644
--- a/jenkins/ci.jpl
+++ b/jenkins/ci.jpl
@@ -507,7 +507,9 @@
       success = false
     } finally {
       archiveArtifacts artifacts: 'tf-m-ci-scripts/lava_artifacts/**', allowEmptyArchive: true
-      emailNotification(success, 'test', filterFailedTest(output))
+      if (all_jobs.size() > 0) {
+        emailNotification(success, 'test', filterFailedTest(output))
+      }
       cleanWs()
       if (!success) {
         error("There was an Error waiting for LAVA jobs")