master_disable_node no longer crashes when given a non-existant node

src/backend/distributed/utils/node_metadata.c

@@ -205,6 +205,10 @@ master_disable_node(PG_FUNCTION_ARGS)
 	CheckCitusVersion(ERROR);
 
 	workerNode = FindWorkerNode(nodeName, nodePort);
+	if (workerNode == NULL)
+	{
+		ereport(ERROR, (errmsg("node at \"%s:%u\" does not exist", nodeName, nodePort)));
+	}
 
 	if (WorkerNodeIsPrimary(workerNode))
 	{

src/test/regress/expected/multi_cluster_management.out

@@ -136,6 +136,9 @@ SELECT master_get_active_worker_nodes();
  (localhost,57637)
 (1 row)
 
+-- try to disable a node which does not exist and see that an error is thrown
+SELECT master_disable_node('localhost.noexist', 2345);
+ERROR:  node at "localhost.noexist:2345" does not exist
 -- restore the node for next tests
 SELECT master_activate_node('localhost', :worker_2_port);
            master_activate_node            

src/test/regress/sql/multi_cluster_management.sql

@@ -52,6 +52,9 @@ INSERT INTO test_reference_table VALUES (1, '1');
 SELECT master_disable_node('localhost', :worker_2_port); 
 SELECT master_get_active_worker_nodes();
 
+-- try to disable a node which does not exist and see that an error is thrown
+SELECT master_disable_node('localhost.noexist', 2345);
+
 -- restore the node for next tests
 SELECT master_activate_node('localhost', :worker_2_port);