apply fails when some data is None
In [91]: from pandas import DataFrame

In [92]: a = DataFrame([1,2, None, 3, 4])

In [93]: a
Out[93]:
      0
0     1
1     2
2  None
3     3
4     4

In [94]: a.apply(lambda x: str(x[0]), axis=1)
Out[94]:
0       1
1       2
2    None
3       3
4       4

In [95]: a.apply(lambda x: int(x[0]), axis=1)
Out[95]:
0     1
1     2
2   NaN
3   NaN
4   NaN

---

I was expecting elements 3 and 4 to still evaluate properly in this case to something like this:

0     1
1     2
2   NaN
3     3
4   4

i am using windows xp 32 bit with pandas 0.7.1 on python 2.7.2
