Remove specific definitions for Union{}

Author: quinnj

src/DataValueInterfaces.jl

@@ -15,7 +15,6 @@ default definition.
 function nondatavaluetype end
 
 nondatavaluetype(::Type{T}) where {T} = T
-nondatavaluetype(::Type{Union{}}) = Union{}
 
 """
     datavaluetype(T)
@@ -32,6 +31,5 @@ default definition.
 function datavaluetype end
 
 datavaluetype(::Type{T}) where {T} = T
-datavaluetype(::Type{Union{}}) = Union{}
 
 end # module