code: func (f *FilterOp) Not(filters ...*FilterOp) *FilterOp {
  	if len(f.NotFilters) == 0 {
  		f.NotFilters = filters[:]
  
  	} else {
  		f.NotFilters = append(f.NotFilters, filters...)
  	}
  
  	return f
  }
docs: // Not will add a NOT op to the filter. One or more FilterOps can be passed in.