If the rpc in `emqx_dashboard_monitor_api:get_collect/1` fails, an
empty map is return. But the current function expects a 4-tuple,
which results in a 500 error returned on such occasions.
```
curl -su admin:public localhost:8888/api/v5/monitor/current | jq .
{
"code": "INTERNAL_ERROR",
"message": "error, function_clause, [{emqx_dashboard_monitor_api,format_current_metrics,[[#{},{0,0,0,0},{0,0,0,0}],{0,0,0,0}],[{file,\"emqx_dashboard_monitor_api.erl\"},{line,179}]},{emqx_dashboard_monitor_api,current_counters,2,[{file,\"emqx_dashboard_monitor_api.erl\"},{line,167}]},{minirest_handler,apply_callback,3,[{file,\"minirest_handler.erl\"},{line,112}]},{minirest_handler,init,2,[{file,\"minirest_handler.erl\"},{line,38}]},{cowboy_handler,execute,2,[{file,\"cowboy_handler.erl\"},{line,41}]},{cowboy_stream_h,execute,3,[{file,\"cowboy_stream_h.erl\"},{line,318}]},{cowboy_stream_h,request_process,3,[{file,\"cowboy_stream_h.erl\"},{line,302}]},{proc_lib,init_p_do_apply,3,[{file,\"proc_lib.erl\"},{line,226}]}]"
}
```
If an empty username or password are given during the initialization
of `emqx_dashboard_admin`, it'll return just the atom `ok`, which
breaks the expected `{ok, _}` in `emqx_dashboard_app:start/2`.
```
{'EXIT',
{{failed_to_start_app,emqx_dashboard,
{emqx_dashboard,
{bad_return,
{{emqx_dashboard_app,start,[normal,[]]},
{'EXIT',
{{badmatch,ok},
[{emqx_dashboard_app,start,2,
[{file,
"/home/thales/dev/emqx/emqx/apps/emqx_dashboard/src/emqx_dashboard_app.erl"},
{line,32}]},
{application_master,start_it_old,4,
[{file,"application_master.erl"},{line,293}]}]}}}}}}}}
```
Deleted the wrapping union.
i.e. previously it's
union([union([...]), array(union([...]))]).
not it's
array(union([...]))
It is after-all a lazy type, and the dynamic check allows
single-elemented arrays not to have `[]` around it.
the old union of array of union schema was just adding confusion
chore(appup): make update_appup.escript output only differences for external dependencies [5.0]
Same as #6307 .
Currently, the update_appup.escript outputs as an error the full appup
file for external dependencies, even if all the changes are already
contained in the depency. Here, we make it only output the missing
actions to be inserted, to aid in seeing what are the differences.
