Method null_count

ruby/red-arrow/lib/arrow/array-statistics.rb:22–29

    if method_defined?(:null_count_exact)
      alias_method :null_count_raw, :null_count
      def null_count
        return nil unless has_null_count?
        if null_count_exact?
          null_count_exact
        else
          null_count_approximate
        end
      end
    end

    if method_defined?(:distinct_count_exact)