Use fill(x[], ()) instead

Author: penelopeysm

src/utils.jl

@@ -290,7 +290,7 @@ function (f::ReshapeTransform)(x)
         # Specially handle the case where x is a singleton array, see
         # https://github.com/JuliaDiff/ReverseDiff.jl/issues/265 and
         # https://github.com/TuringLang/DynamicPPL.jl/issues/698
-        return x[]
+        return fill(x[], ())
     else
         # The call to `tovec` is only needed in case `x` is a scalar.
         return reshape(tovec(x), f.output_size)