convert(::Type{Union{}}, ::String) is ambiguous

[Qiyamah]

WARNING: BinDeps.shlib_ext is deprecated, use Libdl.dlext instead.
  likely near /home/parallels/Projects/GraphViz.jl/deps/build.jl:40
┌ Warning: `Pkg.dir(pkgname, paths...)` is deprecated; instead, do `import Cairo; joinpath(dirname(pathof(Cairo)), "..", paths...)`.
└ @ Pkg.API /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.3/Pkg/src/API.jl:673
ERROR: LoadError: MethodError: convert(::Type{Union{}}, ::String) is ambiguous. Candidates:
  convert(::Type{Union{}}, x) in Base at essentials.jl:166
  convert(::Type{T}, s::AbstractString) where T<:AbstractString in Base at strings/basic.jl:209
  convert(::Type{T}, arg) where T<:VecElement in Base at baseext.jl:8
Possible fix, define
  convert(::Type{Union{}}, ::AbstractString)
Stacktrace:
 [1] convert(::Type{Nothing}, ::String) at ./some.jl:34
 [2] pushfirst!(::Array{Nothing,1}, ::String) at ./array.jl:1103
 [3] generate_steps(::BinDeps.LibraryDependency, ::Autotools, ::Dict{Symbol,Any}) at /home/parallels/.julia/packages/BinDeps/eiJeV/src/dependencies.jl:620
 [4] satisfy!(::BinDeps.LibraryDependency, ::Array{DataType,1}) at /home/parallels/.julia/packages/BinDeps/eiJeV/src/dependencies.jl:944
 [5] satisfy!(::BinDeps.LibraryDependency) at /home/parallels/.julia/packages/BinDeps/eiJeV/src/dependencies.jl:922
 [6] top-level scope at /home/parallels/.julia/packages/BinDeps/eiJeV/src/dependencies.jl:977
 [7] include at ./boot.jl:328 [inlined]
 [8] include_relative(::Module, ::String) at ./loading.jl:1105
 [9] include(::Module, ::String) at ./Base.jl:31
 [10] exec_options(::Base.JLOptions) at ./client.jl:287
 [11] _start() at ./client.jl:460
in expression starting at /home/parallels/Projects/GraphViz.jl/deps/build.jl:46