```
julia> sum([1 2])
3
julia> sum([]) # from math = 0 "by convention"
ERROR: MethodError: no method matching zero(::Type{Any})
Closest candidates are:
zero(::Type{Base.LibGit2.Oid}) at libgit2/oid.jl:88
zero(::Type{Base.Pkg.Resolve.VersionWeights.VWPreBuildItem}) at pkg/resolve/versionweight.jl:80
zero(::Type{Base.Pkg.Resolve.VersionWeights.VWPreBuild}) at pkg/resolve/versionweight.jl:120
...
in _mapreduce(::Base.#identity, ::Base.#+, ::Base.LinearFast, ::Array{Any,1}) at ./reduce.jl:148
in sum(::Array{Any,1}) at ./reduce.jl:229
julia> sum((1, 2))
3
julia> sum((1,))
1
julia> sum((,))
ERROR: syntax: unexpected ,
julia> sum(())
ERROR: StackOverflowError:
in convert(::Type{Union{}}, ::Int64) at ./sysimg.jl:55 (repeats 80000 times)
```

I can see that maybe you want an error. Just not sure.

Not sure how you do the product, but it is defined as 1.