findContours bug?

[liupgd]

using OpenCV
const cv = OpenCV
...
contours = cv.findContours(threshImgBlr2, cv.RETR_LIST, cv.CHAIN_APPROX_NONE)

output:

ERROR: MethodError: no method matching jlopencv_core_Mat_mutable_data(::OpenCV.CxxMatDereferenced)
Closest candidates are:
jlopencv_core_Mat_mutable_data(::Union{CxxWrap.CxxWrapCore.SmartPointer{T2}, T2} where T2<:OpenCV.CxxMatAllocated) at /home/.../.julia/packages/CxxWrap/OcN1Z/src/CxxWrap.jl:618
Stacktrace:
[1] cpp_to_julia(mat::OpenCV.CxxMatDereferenced)
@ OpenCV ~/.julia/artifacts/7f7ecae944127299b78b8a360c8b5a5f94df8b2f/OpenCV/src/mat_conversion.jl:20
[2] cpp_to_julia
@ ~/.julia/artifacts/7f7ecae944127299b78b8a360c8b5a5f94df8b2f/OpenCV/src/mat_conversion.jl:103 [inlined]
[3] cpp_to_julia
@ ~/.julia/artifacts/7f7ecae944127299b78b8a360c8b5a5f94df8b2f/OpenCV/src/cv_cxx.jl:38 [inlined]
[4] findContours
@ ~/.julia/artifacts/7f7ecae944127299b78b8a360c8b5a5f94df8b2f/OpenCV/src/cv_cxx_wrap.jl:2232 [inlined]
[5] #findContours#226
@ ~/.julia/artifacts/7f7ecae944127299b78b8a360c8b5a5f94df8b2f/OpenCV/src/cv_cxx_wrap.jl:2234 [inlined]
[6] findContours(image::OpenCV.Mat{UInt8}, mode::Int32, method::Int32)
@ OpenCV ~/.julia/artifacts/7f7ecae944127299b78b8a360c8b5a5f94df8b2f/OpenCV/src/cv_cxx_wrap.jl:2234
[7] top-level scope
@ REPL[220]:1

Thx