patch 8.2.3359: Vim9: error for type when variable is not set

Problem:    Vim9: error for type when variable is not set.
Solution:   Give a specific error for a NULL function. (closes #8773)
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index 0ffe686..f0c4c0d 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -2696,6 +2696,15 @@
       assert_equal('ooooo', RepeatFunc(5))
   END
   CheckDefAndScriptSuccess(lines)
+
+  lines =<< trim END
+      vim9script
+      def Foo(Parser: any)
+      enddef
+      var Expr: func(dict<any>): dict<any>
+      const Call = Foo(Expr)
+  END
+  CheckScriptFailure(lines, 'E1235:')
 enddef
 
 def Test_cmd_modifier()