MethodError if variable `fld` defined before using BenchmarkTools

[jaakkor2]

fld = ""
using BenchmarkTools
@btime a=1

gives

ERROR: MethodError: objects of type String are not callable
Stacktrace:
 [1] ##sample#260(::BenchmarkTools.Parameters) at C:\Users\jaakkor2\.julia\packages\BenchmarkTools\eCEpo\src\execution.jl:386
 [2] _run(::BenchmarkTools.Benchmark{Symbol("##benchmark#258")}, ::BenchmarkTools.Parameters; verbose::Bool, pad::String, kwargs::Base.Iterators.Pairs{Symbol,Integer,NTuple{4,Symbol},NamedTuple{(:samples, :evals, :gctrial, :gcsample),Tuple{Int64,Int64,Bool,Bool}}}) at C:\Users\jaakkor2\.julia\packages\BenchmarkTools\eCEpo\src\execution.jl:405
 [3] (::Base.var"#inner#2"{Base.Iterators.Pairs{Symbol,Integer,NTuple{5,Symbol},NamedTuple{(:verbose, :samples, :evals, :gctrial, :gcsample),Tuple{Bool,Int64,Int64,Bool,Bool}}},typeof(BenchmarkTools._run),Tuple{BenchmarkTools.Benchmark{Symbol("##benchmark#258")},BenchmarkTools.Parameters}})() at .\essentials.jl:713
 [4] #invokelatest#1 at .\essentials.jl:714 [inlined]
 [5] #run_result#37 at C:\Users\jaakkor2\.julia\packages\BenchmarkTools\eCEpo\src\execution.jl:32 [inlined]
 [6] run(::BenchmarkTools.Benchmark{Symbol("##benchmark#258")}, ::BenchmarkTools.Parameters; progressid::Nothing, nleaves::Float64, ndone::Float64, kwargs::Base.Iterators.Pairs{Symbol,Integer,NTuple{5,Symbol},NamedTuple{(:verbose, :samples, :evals, :gctrial, :gcsample),Tuple{Bool,Int64,Int64,Bool,Bool}}}) at C:\Users\jaakkor2\.julia\packages\BenchmarkTools\eCEpo\src\execution.jl:94
 [7] #warmup#45 at C:\Users\jaakkor2\.julia\packages\BenchmarkTools\eCEpo\src\execution.jl:141 [inlined]
 [8] warmup(::BenchmarkTools.Benchmark{Symbol("##benchmark#258")}) at C:\Users\jaakkor2\.julia\packages\BenchmarkTools\eCEpo\src\execution.jl:141
 [9] top-level scope at C:\Users\jaakkor2\.julia\packages\BenchmarkTools\eCEpo\src\execution.jl:481

Julia v1.5.3, BenchmarkTools v0.5.0