test: add cases for blank rpcauth

Author: tdb3

test/functional/rpc_users.py

@@ -139,9 +139,11 @@ def run_test(self):
         init_error = 'Error: Unable to start HTTP server. See debug log for details.'
 
         self.log.info('Check -rpcauth are validated')
-        # Empty -rpcauth= are ignored
+        self.log.info('Empty -rpcauth are ignored')
+        self.restart_node(0, extra_args=['-rpcauth'])
         self.restart_node(0, extra_args=['-rpcauth='])
         self.stop_node(0)
+        self.nodes[0].assert_start_raises_init_error(expected_msg=init_error, extra_args=['-rpcauth=""'])
         self.nodes[0].assert_start_raises_init_error(expected_msg=init_error, extra_args=['-rpcauth=foo'])
         self.nodes[0].assert_start_raises_init_error(expected_msg=init_error, extra_args=['-rpcauth=foo:bar'])
         self.nodes[0].assert_start_raises_init_error(expected_msg=init_error, extra_args=['-rpcauth=foo:bar:baz'])