patch 8.2.0493: Vim9: some error messages not tested

Problem:    Vim9: some error messages not tested.
Solution:   Add more tests.  Fix uncovered bugs.
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 5f290aa..6832bf1 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -290,7 +290,8 @@
 {
     return &t_string;
 }
-    static type_T * ret_list_any(int argcount UNUSED, type_T **argtypes UNUSED)
+    static type_T *
+ret_list_any(int argcount UNUSED, type_T **argtypes UNUSED)
 {
     return &t_list_any;
 }
@@ -330,9 +331,14 @@
     return &t_blob;
 }
     static type_T *
-ret_partial_void(int argcount UNUSED, type_T **argtypes UNUSED)
+ret_func_any(int argcount UNUSED, type_T **argtypes UNUSED)
 {
-    return &t_partial_void;
+    return &t_func_any;
+}
+    static type_T *
+ret_partial_any(int argcount UNUSED, type_T **argtypes UNUSED)
+{
+    return &t_partial_any;
 }
     static type_T *
 ret_channel(int argcount UNUSED, type_T **argtypes UNUSED)
@@ -558,7 +564,7 @@
     {"foldtext",	0, 0, 0,	  ret_string,	f_foldtext},
     {"foldtextresult",	1, 1, FEARG_1,	  ret_string,	f_foldtextresult},
     {"foreground",	0, 0, 0,	  ret_void,	f_foreground},
-    {"funcref",		1, 3, FEARG_1,	  ret_partial_void, f_funcref},
+    {"funcref",		1, 3, FEARG_1,	  ret_partial_any, f_funcref},
     {"function",	1, 3, FEARG_1,	  ret_f_function, f_function},
     {"garbagecollect",	0, 1, 0,	  ret_void,	f_garbagecollect},
     {"get",		2, 3, FEARG_1,	  ret_any,	f_get},
@@ -952,9 +958,10 @@
     {"test_null_blob",	0, 0, 0,	  ret_blob,	f_test_null_blob},
     {"test_null_channel", 0, 0, 0,	  ret_channel,	JOB_FUNC(f_test_null_channel)},
     {"test_null_dict",	0, 0, 0,	  ret_dict_any,	f_test_null_dict},
+    {"test_null_function", 0, 0, 0,	  ret_func_any,	f_test_null_function},
     {"test_null_job",	0, 0, 0,	  ret_job,	JOB_FUNC(f_test_null_job)},
     {"test_null_list",	0, 0, 0,	  ret_list_any,	f_test_null_list},
-    {"test_null_partial", 0, 0, 0,	  ret_partial_void, f_test_null_partial},
+    {"test_null_partial", 0, 0, 0,	  ret_partial_any, f_test_null_partial},
     {"test_null_string", 0, 0, 0,	  ret_string,	f_test_null_string},
     {"test_option_not_set", 1, 1, FEARG_1,ret_void,	 f_test_option_not_set},
     {"test_override",	2, 2, FEARG_2,	  ret_void,	f_test_override},