update cleanup

src/optimise/train.jl

@@ -7,14 +7,12 @@ function update!(x::AbstractArray, x̄)
 end
 
 function update!(opt, x, x̄)
-  if x̄ == nothing
-    x̄ = zeros(size(x)...)
-  end
-  update!(x, -apply!(opt, x, x̄))
+  x .-= apply!(opt, x, x̄)
 end
 
 function update!(opt, xs::Params, gs)
   for x in xs
+    gs[x] == nothing && continue
     update!(opt, x, gs[x])
   end
 end
@@ -25,6 +23,7 @@ runall(f) = f
 runall(fs::AbstractVector) = () -> foreach(call, fs)
 
 struct StopException <: Exception end
+
 """
     stop()