Problem description: 

Steps to reproduce:
1. Set cell A1 to 1
2. Set cell A2 to ="" (empty string)
3. Set cell A3 to =A1+A2
4. Set cell A4 to =value("")
5. Set cell A5 to =A1+B1 (B1 is an empty cell)
6. Set cell A6 to =value(B1)
Current behavior:
-A3 returns #VALUE
-A4 returns err:502
-A5 returns 1
-A6 returns 0

Expected behavior:
Openoffice 3.3 returns
-A3:returns 1
-A4:returns err:502
-A5:returns 1
-A6:returns 0

Conclusion:
An empty cell and a cell with empty sting should return either err:502 or 0, not a mix of both. My preference is 0 for historic reasons, but a setting to choose behaviour may be even better. I guess this topic is open to opinions.
(err:502 is "Invalid argument")

Platform (if different from the browser): 
              
Browser: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; .NET4.0E)