julia

f6e911aa - make `ml_matches` return `nothing` when there are too many matches (#44478)

make `ml_matches` return `nothing` when there are too many matches (#44478) Continuation from <https://github.com/JuliaLang/julia/pull/44448#discussion_r820025006>. Previously `ml_matches` (and its dependent utilities like `_methods_by_ftype`) returned `false` for cases when there are too many matching method, but its consumer like `findall(::Type, ::InternalMethodTable)` usually handles such case as `missing`. This commit does a refactor so that they all use the more consistent value `nothing` for representing that case.