somehow DataFrame
calls promote_type(:Type{Union{}}, ::Type{T})
indirectly for T = String
.
promote_type(::Type{Union{}}, ::Type{T}) where T in Base at promotion.jl:224
But WeakRefString.jl
defined the below, causing an ambiguity cos Union{} <: InlineString
is true
.
promote_type(::Type{T}, ::Type{String}) where T<:InlineString in WeakRefStrings at c:\git\WeakRefStrings\src\inlinestrings.jl:44