How to suppress "No matching autocommands"?

Question

I have a log library that has a autocmd log User hook, to show saved log or set it to a dedicated scratch buffer or etc.

It works quite well, but there is slight nuisance. When inspection/debug done, I clear the hook by au! log User. But then No matching autocommands: log User will show at cmdline constantly. Since the log#log function invoke doa log User.

Problem:
Is there a way to suppress the No matching autocommands: log User message when doa log User but no log User autocmd being set.
Or is there a function to check existence of a specified autocmd, if no one, then do not doa (to avoid No matching autocommands noise).

Failed attempts:

• use sil doa, then hook that just echoes will never work. Unacceptable.

Answer 1

Thx to Matt's comment. Found the answer in :h exists.

the relevant part is.

    #event      autocommand defined for this event
    #event#pattern  autocommand defined for this event and
                    pattern (the pattern is taken
                    literally and compared to the
                    autocommand patterns character by
                    character)
    #group      autocommand group exists
    #group#event    autocommand defined for this group and
                    event.
    #group#event#pattern
                    autocommand defined for this group,
                    event and pattern.
    ##event     autocommand for this event is
                    supported.

thus answer for my case is

    if exists('#log#User')
        doa log User
    endif