Scanner input == null?

I am trying to say if you enter a character it will do this; else if scanner input == null do this instead. I'm not getting any syntax errors, I just need to know how to word this so that if you don't enter any characters and hit ENTER then it will go to my default settings. Here is what I have so far.

Shape sq = new Square(10);
                System.out.println("Choose character to fill your shape. A-Z, a-z, ! # $ % & ( ) * + Press ENTER.");
                characterChoiceSquare = input.next();
                if(characterChoiceSquare == input.next())
                {
                    for(int m = 0; m < shapeChars.length; m++)
                    }
                    {
                        if(characterChoiceSquare.equals(shapeChars[m]));
                        {
                            char[] c1 = characterChoiceSquare.toCharArray();
                            char[] shapeCharacter = new char[sq.getSizeInt()];
                            for(int i = 0; i < sq.getSizeInt(); i++) 
                            {
                                shapeCharacter[i] = c1[0]; // repeat the char input to fit shapeString
                            }
                            string = String.valueOf(shapeCharacter); //assign the value of the arraylist to shapeString

                            shapeString += string + "\n";

                            System.out.print(shapeString);
                        }
                    }
                }
                else if(characterChoiceSquare == null)
                {
                    System.out.print(sq.displayCharacters());
                }