Functions to check nil or null object input for NSNumber and NSString.

UnNull.h

/**
 Inspect input number to see if there is nil input or null object input
 
 @param aNumber an input number
 
 @return If nil input or null object input found, a NSNumber object with zero value will return.
 If the input is a NSStirng object, a NSNumber object contianing dobleValue of the string will return.
 
 @warning If input number is not a NSNumber or NSString, a NSNumber object containing zero will return.
 */
NSNumber* Number(id aNumber);


/**
 Inspect input string to see if there is nil input or null object input
 
 @param aString an input string
 
 @return If nil input or null object input found, a <null> string will return.
 If the input is a NSNumber object, a NSString object contianing dobleValue of the number will return.
 
 @warning If input string is not a NSString or NSNumber, a <null> string will return.
 */
NSString* String(id aString);

UnNull.m

NSNumber* Number(id aNumber)
{
    if (!aNumber) {
        NSLog(@"Error: Input is nil while inspecting the number");
        return @(0);
    }
    
    if ([aNumber isKindOfClass:[NSNull class]]) {
        NSLog(@"Error: Input number is a NSNull object.");
        return @(0);
    }
    
    if ([aNumber isKindOfClass:[NSString class]]) {
        NSLog(@"Warning: Converted %@ to a NSNumber class", NSStringFromClass([aNumber class]));
        double doubleVal = [aNumber doubleValue];
        return @(doubleVal);
    }
    else if ([aNumber isKindOfClass:[NSNumber class]]) {
        return aNumber;
    }
    else {
        NSLog(@"Error: Can not transform %@ to NSNumber. Return Zero value.", NSStringFromClass([aNumber class]));
        return @(0);
    }
}

NSString* String(id aString)
{
    if (!aString) {
        NSLog(@"Error: Input is a nil while inspecting the string.");
        return @"<null>";
    }
    
    if ([aString isKindOfClass:[NSNull class]]) {
        NSLog(@"Error: Input string is a NSNull object.");
        return @"<null>";
    }
    
    if ([aString isKindOfClass:[NSNumber class]]) {
        NSLog(@"Warning: Converted %@ to a NSString class", NSStringFromClass([aString class]));
        double doubleVal = [aString doubleValue];
        return [NSString stringWithFormat:@"%f", doubleVal];
    }
    else if ([aString isKindOfClass:[NSString class]]) {
        return aString;
    }
    else {
        NSLog(@"Error: Can not transform %@ to NSString. Return <null> string.", NSStringFromClass([aString class]));
        return @"<null>";
    }
}