remove sector, define TrivialSector()

Author: ogauthe

NDTensors/src/lib/Sectors/src/category_product.jl

@@ -16,6 +16,7 @@ CategoryProduct(c::CategoryProduct) = _CategoryProduct(categories(c))
 categories(s::CategoryProduct) = s.cats
 
 const TrivialSector = CategoryProduct{Tuple{}}
+TrivialSector() = CategoryProduct(())
 
 # =================================  Sectors interface  ====================================
 function SymmetryStyle(c::CategoryProduct)
@@ -122,8 +123,6 @@ function recover_category_product_type(T::Type, cats::Tuple{Vararg{AbstractCateg
   return CategoryProduct(T(cats))
 end
 
-sector(args...; kws...) = CategoryProduct(args...; kws...)
-
 # =================================  Cartesian Product  ====================================
 ×(c1::AbstractCategory, c2::AbstractCategory) = ×(CategoryProduct(c1), CategoryProduct(c2))
 function ×(p1::CategoryProduct, p2::CategoryProduct)