Error in planar contractions with sum

[lkdvos]

The following MWE leads to a LoadError, I have not investigated further. It seems to be related to the sum though.

using TensorKit
@planar D[i; j] := A[i; j] + B[i; k] * C[k; j]

ERROR: LoadError: MethodError: no method matching iterate(::Symbol)
The function `iterate` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  iterate(::LazyString)
   @ Base strings/lazy.jl:94
  iterate(::LazyString, ::Integer)
   @ Base strings/lazy.jl:95
  iterate(::Base.EnvDict)
   @ Base env.jl:216
  ...

Stacktrace:
  [1] _construct_braidingtensors!(ex::Any, preargs::Any, indexmap::Any)
    @ TensorKit ~/.julia/packages/TensorKit/9IxV4/src/planar/preprocessors.jl:218
  [2] _construct_braidingtensors(ex::Any)
    @ TensorKit ~/.julia/packages/TensorKit/9IxV4/src/planar/preprocessors.jl:95
  [3] iterate
    @ ./generator.jl:48 [inlined]
  [4] collect_to!(dest::Vector{…}, itr::Base.Generator{…}, offs::Int64, st::Int64)
    @ Base ./array.jl:849
  [5] collect_to_with_first!(dest::Vector{…}, v1::Expr, itr::Base.Generator{…}, st::Int64)
    @ Base ./array.jl:827
  [6] _collect(c::Vector{…}, itr::Base.Generator{…}, ::Base.EltypeUnknown, isz::Base.HasShape{…})
    @ Base ./array.jl:821
  [7] collect_similar(cont::Vector{Any}, itr::Base.Generator{Vector{Any}, typeof(TensorKit._construct_braidingtensors)})
    @ Base ./array.jl:720
  [8] map(f::Function, A::Vector{Any})
    @ Base ./abstractarray.jl:3371
  [9] _construct_braidingtensors(ex::Any)
    @ TensorKit ~/.julia/packages/TensorKit/9IxV4/src/planar/preprocessors.jl:111
 [10] (::TensorOperations.TensorParser)(ex::Expr)
    @ TensorOperations ~/.julia/packages/TensorOperations/RaU9j/src/indexnotation/parser.jl:27
 [11] var"@planar"(__source__::LineNumberNode, __module__::Module, args::Vararg{Expr})
    @ TensorKit ~/.julia/packages/TensorKit/9IxV4/src/planar/macros.jl:9