Return a null pointer. Note that this method has the same return type as the allocator-aware version so that the remainder of the implementation of bsl::variant is abstracted with respect to whether or not the specialization is allocator-aware; this is why both methods return bslma::Allocator* instead of bsl::allocator<char>. The returned pointer will be ignored (and not dereferenced) when passed to bslma::ConstructionUtil::construct.