The fallback treats the first argument as a function apparently?? ```julia julia> mean(Union{Int,Missing}[1,2,3], weights([1,2,3])) 4.666666666666667 julia> @which mean(Union{Int,Missing}[1,2,3], weights([1,2,3])) mean(f, A::AbstractArray) in Statistics at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.1/Statistics/src/Statistics.jl:76 ```