def convert(*filters)
      block_given? ? dup.convert!(*filters, &Proc.new) : dup.convert!(*filters)
    end
def convert(*filters)
      block_given? ? dup.convert!(*filters, &Proc.new) : dup.convert!(*filters)
    end
Returns a duplicate entry with all values converted using the filter(s).
 If an optional block is given, only those values will be converted where
 the block returns true (the block will be called with each key-value pair).

 @see #convert!