Don't attempt to parse workflow if it doesn't exist (opensearch-project#1346)

Signed-off-by: Chase Engelbrecht <[email protected]>

Author: engechas

alerting/src/main/kotlin/org/opensearch/alerting/transport/TransportDeleteWorkflowAction.kt

@@ -119,7 +119,7 @@ class TransportDeleteWorkflowAction @Inject constructor(
     ) {
         suspend fun resolveUserAndStart() {
             try {
-                val workflow = getWorkflow()
+                val workflow: Workflow = getWorkflow() ?: return
 
                 val canDelete = user == null ||
                     !doFilterForUser(user) ||
@@ -296,17 +296,27 @@ class TransportDeleteWorkflowAction @Inject constructor(
             return deletableMonitors
         }
 
-        private suspend fun getWorkflow(): Workflow {
+        private suspend fun getWorkflow(): Workflow? {
             val getRequest = GetRequest(ScheduledJob.SCHEDULED_JOBS_INDEX, workflowId)
 
             val getResponse: GetResponse = client.suspendUntil { get(getRequest, it) }
-            if (getResponse.isExists == false) {
-                actionListener.onFailure(
-                    AlertingException.wrap(
-                        OpenSearchStatusException("Workflow not found.", RestStatus.NOT_FOUND)
-                    )
-                )
+            if (!getResponse.isExists) {
+                handleWorkflowMissing()
+                return null
             }
+
+            return parseWorkflow(getResponse)
+        }
+
+        private fun handleWorkflowMissing() {
+            actionListener.onFailure(
+                AlertingException.wrap(
+                    OpenSearchStatusException("Workflow not found.", RestStatus.NOT_FOUND)
+                )
+            )
+        }
+
+        private fun parseWorkflow(getResponse: GetResponse): Workflow {
             val xcp = XContentHelper.createParser(
                 xContentRegistry, LoggingDeprecationHandler.INSTANCE,
                 getResponse.sourceAsBytesRef, XContentType.JSON