Constant functions error

[mohamed82008]

julia> Tracker.gradient((x)->(1.0), [0.5])
ERROR: MethodError: no method matching back!(::Float64)
Closest candidates are:
  back!(::Any, ::Any; once) at C:\Users\user\.julia\packages\Tracker\SAr25\src\back.jl:75
  back!(::Tracker.TrackedReal; once) at C:\Users\user\.julia\packages\Tracker\SAr25\src\lib\real.jl:14
  back!(::TrackedArray) at C:\Users\user\.julia\packages\Tracker\SAr25\src\lib\array.jl:68
Stacktrace:
 [1] gradient_(::Function, ::Array{Float64,1}) at C:\Users\user\.julia\packages\Tracker\SAr25\src\back.jl:4
 [2] #gradient#24 at C:\Users\user\.julia\packages\Tracker\SAr25\src\back.jl:164 [inlined]
 [3] gradient(::Function, ::Array{Float64,1}) at C:\Users\user\.julia\packages\Tracker\SAr25\src\back.jl:164
 [4] top-level scope at none:0