IEnumerable.defaultIfEmpty Method
        
 Returns the elements of the sequence or the specified value in a singleton collection if the sequence is empty.
 
         
        Parameters
        
            - defaultValue
            
 
            - 
                
Type: Object
The value to return if this sequence is empty. 
        
        Return Value
        
Type: IEnumerable
        
An enumerable that contains defaultValue if this sequence is empty; otherwise, this sequence.