Java Programming

Hi,
I am running a method, which returns a String value, and its function body is something like this:

public String methodName(int, int)
{
try{
  String data = check for string at location(int, int);
// "check" returns the value at particular location that i am storing in "data" variable
if(data ==NULL)
    return (String)(" ");
else 
    return data;
}catch
{
   //  print(error message);
// whatever
}

So, my problem is at line if(data==NULL)

i am not sure about, how to check the string with null value...
Right now i am getting the error message from Catch due to some exception in the try body.
If you got any idea about this matter then your help would be appreciated.

Thanks,
Ashish