Domain error when inferring array type in 0-length degenerated case

Hi!

do you plan to support degenerated cases like the one below in the future?

Just for curiosity, how would you fix this in the library? Is it possible to fix it without calling something like Base._return_type?

Thanks for the help!

julia> using MappedArrays

julia> a = fill(1,0)
0-element Array{Int64,1}

julia> f(x) = sqrt(x-1)
f (generic function with 1 method)

julia> mappedarray(f,a)
ERROR: DomainError with -1.0:
sqrt will only return a complex result if called with a complex argument. Try sqrt(Complex(x)).
Stacktrace:
 [1] throw_complex_domainerror(::Symbol, ::Float64) at ./math.jl:31
 [2] sqrt at ./math.jl:493 [inlined]
 [3] sqrt at ./math.jl:519 [inlined]
 [4] f at ./REPL[3]:1 [inlined]
 [5] mappedarray(::typeof(f), ::Array{Int64,1}) at /home/fverdugo/.julia/packages/MappedArrays/8HESW/src/MappedArrays.jl:61
 [6] top-level scope at REPL[4]:1

Start with the mappedarray entry point in src/MappedArrays.jl:61 and reproduce the empty-array example using MappedArrays and sqrt(x-1). Determine how the result type is inferred for a zero-length array and whether the reported DomainError can be avoided without Base._return_type; done means the degenerate case is handled with an agreed result type and behavior.