Error "THIS SHOULDN'T HAPPEN" for @vlplot()

[Leonhard Lücken]

I'm not sure, if this is worth reporting, but since the error is shouting, I thought it couldn't hurt.

using VegaLite
@vlplot(Dict(:a=>1, :b=>"3"))

gives

ERROR: THIS SHOULDN'T HAPPEN Dict{Symbol, Any}(:a => 1, :b => "3")
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:35
 [2] replace_remaining_frag(frag::Dict{Symbol, Any})
   @ Vega ~/.julia/packages/Vega/NBNbC/src/dsl_vlplot_function/dsl_vlplot_function.jl:55
 [3] (::VegaLite.var"#36#38")(::Pair{String, Dict{Symbol, Any}})
   @ VegaLite ./none:0
 [4] iterate
   @ ./generator.jl:47 [inlined]
 [5] OrderedCollections.OrderedDict{String, Any}(kv::Base.Generator{OrderedCollections.OrderedDict{String, Any}, VegaLite.var"#36#38"})
   @ OrderedCollections ~/.julia/packages/OrderedCollections/SInLM/src/ordered_dict.jl:28
 [6] convert_frag_tree_to_dict(spec::VegaLite.VLFrag)
   @ VegaLite ~/.julia/packages/VegaLite/wEePk/src/dsl_vlplot_function/dsl_vlplot_function.jl:220
 [7] top-level scope
   @ REPL[2]:1

Julia version 1.9.2
VegaLite v3.2.2