Cannot write Char array

[lstagner]

julia> using MAT

julia> a = fill(' ',(3,3))
3×3 Array{Char,2}:
 ' '  ' '  ' '
 ' '  ' '  ' '
 ' '  ' '  ' '

julia> matwrite("test.mat",Dict("a"=>a))
ERROR: This is the write function for CompositeKind, but the input doesn't fit
Stacktrace:
 [1] error(::String) at ./error.jl:33
 [2] m_write(::MAT.MAT_HDF5.MatlabHDF5File, ::HDF5.HDF5Group, ::String, ::Char) at /Users/lstagner/.julia/packages/MAT/XPntV/src/MAT_HDF5.jl:529
 [3] m_write(::MAT.MAT_HDF5.MatlabHDF5File, ::HDF5.HDF5File, ::String, ::Array{Char,2}) at /Users/lstagner/.julia/packages/MAT/XPntV/src/MAT_HDF5.jl:478
 [4] write(::MAT.MAT_HDF5.MatlabHDF5File, ::String, ::Array{Char,2}) at /Users/lstagner/.julia/packages/MAT/XPntV/src/MAT_HDF5.jl:545
 [5] #matwrite#4(::Bool, ::typeof(matwrite), ::String, ::Dict{String,Array{Char,2}}) at /Users/lstagner/.julia/packages/MAT/XPntV/src/MAT.jl:157
 [6] matwrite(::String, ::Dict{String,Array{Char,2}}) at /Users/lstagner/.julia/packages/MAT/XPntV/src/MAT.jl:148
 [7] top-level scope at REPL[36]:1