patch 9.1.0481: Vim9: term_getjob() throws an exception on error

Problem:  Vim9: term_getjob() throws an exception on error
Solution: Return null_job instead, when there is no job
          (Ernie Rael)

closes: #14984

Signed-off-by: Ernie Rael <errael@raelity.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_vim9_builtin.vim b/src/testdir/test_vim9_builtin.vim
index 3200b73..6b1a50d 100644
--- a/src/testdir/test_vim9_builtin.vim
+++ b/src/testdir/test_vim9_builtin.vim
@@ -4557,6 +4557,7 @@
 def Test_term_getjob()
   CheckRunVimInTerminal
   v9.CheckSourceDefAndScriptFailure(['term_getjob(0z10)'], ['E1013: Argument 1: type mismatch, expected string but got blob', 'E1220: String or Number required for argument 1'])
+  v9.CheckSourceDefAndScriptSuccess(['assert_true(term_getjob(0) == null_job)'])
 enddef
 
 def Test_term_getline()