First Letter to Appear Twice LeetCode solution in Java

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class Solution {
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  public char repeatedCharacter(String s) {
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    HashSet<Character> set = new HashSet<>(); // Create a set of characters
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    for (int i = 0; i < s.length(); i++) {
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      if (set.contains(s.charAt(i)))
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        return s.charAt(
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            i); // If the set already contains the current character, then it is the required ans
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      set.add(s.charAt(i));
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    }
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    return 'a'; // As it is given in the question that there is at least one letter that appears
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    // twice, therefore it is certain that the ans will be found before we reach this
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    // statement. So, just adding any random return statement so that there is no error
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    // in the code.
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  }
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}