ERROR: MethodError: no method matching zero(::Type{Any})
Closest candidates are:
  zero(::Type{Union{Missing, T}}) where T at missing.jl:105
  zero(::Type{Missing}) at missing.jl:103
  zero(::Type{LibGit2.GitHash}) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.4/LibGit2/src/oid.jl:220
  ...
Stacktrace:
 [1] zero(::Type{Any}) at ./missing.jl:105
 [2] reduce_empty(::typeof(+), ::Type{T} where T) at ./reduce.jl:306
 [3] reduce_empty(::typeof(Base.add_sum), ::Type{T} where T) at ./reduce.jl:313
 [4] mapreduce_empty(::typeof(identity), ::Function, ::Type{T} where T) at ./reduce.jl:335
 [5] _mapreduce(::typeof(identity), ::typeof(Base.add_sum), ::IndexLinear, ::Array{Any,1}) at ./reduce.jl:392
 [6] _mapreduce_dim at ./reducedim.jl:312 [inlined]
 [7] #mapreduce#580 at ./reducedim.jl:307 [inlined]
 [8] mapreduce at ./reducedim.jl:307 [inlined]
 [9] _sum at ./reducedim.jl:657 [inlined]
 [10] _sum at ./reducedim.jl:656 [inlined]
 [11] #sum#583 at ./reducedim.jl:652 [inlined]
 [12] sum at ./reducedim.jl:652 [inlined]
 [13] polynomial!(::Array{Any,1}, ::MultivariatePolynomials.SortedState) at /Users/gerickf/.julia/packages/MultivariatePolynomials/fixWm/src/polynomial.jl:64
 [14] differentiate(::Polynomial{Sym,Term{Sym,Monomial{(x,),1}},Array{Term{Sym,Monomial{(x,),1}},1}}, ::Variable{:x}) at /Users/gerickf/.julia/packages/MultivariatePolynomials/fixWm/src/differentiation.jl:40
 [15] top-level scope at REPL[8]:1