C++/CLI -- what about NULL?

Some of the code I'm upgrading to C++/CLI (.Net 2+) from Managed Extensions for C++ (.Net 1.1) compares an object to NULL or 0 to determine whether it's a null pointer.

But I'm getting a compile error on these lines.  
Cannot convert from 'int' to 'System::Drawing::Bitmap^'

Below is one of the functions in which I use the technique and get the error ... about 3 spots in this one.

What is the C++/CLI way to do this?

Thanks!

Bitmap ^ MyClass::LoadBMP(String ^fileName) {
 
		if(fileName == NULL || fileName == String::Empty) {                  // Make Sure A Filename Was Given
			return NULL;                                                    // If Not Return Null
		}
 
		// Make Sure The File Exists In One Of The Usual Directories
		if(!File::Exists(fileName)) {
			return NULL;                                                    // If Not Return Null
		}
 
		if(File::Exists(fileName)) {                                         // Does The File Exist Here?
			return gcnew Bitmap(fileName);                                    // Load The Bitmap
    }
}

Select allOpen in new window