check_ambiguous_visitor assertion

[DatName]

julia> versioninfo()
    Julia Version 0.6.4
    Commit 9d11f62bcb (2018-07-09 19:09 UTC)
    DEBUG build
    Platform Info:
      OS: Linux (x86_64-pc-linux-gnu)
      CPU: Intel(R) Core(TM) i7-7740X CPU @ 4.30GHz
      WORD_SIZE: 64
      BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Haswell MAX_THREADS=16)
      LAPACK: libopenblas64_
      LIBM: libopenlibm
      LLVM: libLLVM-3.9.1 (ORCJIT, broadwell)
julia> using KernelDensity
INFO: Precompiling module KernelDensity.
julia-debug: /buildworker/worker/package_linux64/build/src/gf.c:1132: check_ambiguous_visitor: Assertion `!jl_subtype((jl_value_t*)sig, (jl_value_t*)type)' failed.

signal (6): Aborted
while loading ~/.julia/v0.6/KernelDensity/src/KernelDensity.jl, in expression starting on line 9

This happening both on

julia> Pkg.status("KernelDensity")
 - KernelDensity                 0.4.1

and master.