NSNumberFormatter leaks on NSCFNumber getObjectValue

I created a common method "isValidAmount" to check if the user inputs a correct amount in UITextField. This is working, but the problem is, I am getting开发者_JAVA百科 leaks when the number is invalid. The leaked object is "NSCFNumber" and the responsible for that is "getObjectValue". I don't know what else to do. I already release the "formatter" below. I even tried to release "number" below. But still I keep on getting this leak. Please help.

+ (BOOL) isValidAmount:(NSString *)amount {
    NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
    [formatter setNumberStyle:NSNumberFormatterDecimalStyle];
    NSNumber *number = [formatter numberFromString:amount];
    [formatter release];
    if (!number) {
        return NO;
    }
    return YES;
}

By inspection, there is nothing wrong with that code.

Does it also leak on the device? Can you post the exact backtrace of the allocation that is leaked?