How can I declare an empty zoo object?

Hi,

#Without indices

 xzoo<-zoo()
 x1zoo_f<-zoo(1:10,)
 cbind(xzoo,x1zoo_f)
   x1zoo_f
1        1
2        2
3        3
4        4
5        5
6        6
7        7
8        8
9        9
10      10


#With indices on one
x1zoo_f<-zoo(1:5,1:10)

cbind(xzoo,x1zoo_f)

   x1zoo_f
1        1
2        2
3        3
4        4
5        5
6        1
7        2
8        3
9        4
10       5

#with a different index.  Here, I get warning message.

 x1zoo_f<-zoo(1:5,c(5,6,8,11,13))

cbind(xzoo,x1zoo_f)

   x1zoo_f
5        1
6        2
8        3
11       4
13       5
Warning message:
In merge.zoo(..., all = all, fill = fill, suffixes = suffixes, retclass = "zoo",  :
  Index vectors are of different classes: integer numeric