Replace Repeating Chars

import java.util.Scanner;

public class ReplaceRepeatingChars {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        String letter = scanner.nextLine().trim();

        StringBuilder sequence = new StringBuilder();


        if (letter == null || letter.length() == 0) {
            return;
        }
        char previousSymbol = letter.charAt(0);
        sequence.append(previousSymbol);

        for (int index = 1; index < letter.length(); index++) {
            char symbol = letter.charAt(index);
            if (symbol != previousSymbol) {
                sequence.append(symbol);
                previousSymbol = symbol;
            }
        }
        System.out.println(sequence);
    }
}