fix: add braces to satisfy Checkstyle NeedBraces rule

Author: Ruturaj-007

src/main/java/com/thealgorithms/stacks/ValidParentheses.java

@@ -4,9 +4,6 @@
 import java.util.Deque;
 import java.util.Map;
 
-/**
- * Utility class to check if a string has valid parentheses.
- */
 public final class ValidParentheses {
 
     private ValidParentheses() {
@@ -15,20 +12,19 @@ private ValidParentheses() {
 
     private static final Map<Character, Character> PAIRS = Map.of(')', '(', '}', '{', ']', '[');
 
-    /**
-     * Checks if the input string has valid parentheses.
-     *
-     * @param s the input string
-     * @return true if valid, false otherwise
-     */
     public static boolean isValid(final String s) {
-        if (s == null) throw new NullPointerException("Input cannot be null");
+        if (s == null) {
+            throw new NullPointerException("Input cannot be null");
+        }
+
         Deque<Character> stack = new ArrayDeque<>();
         for (char ch : s.toCharArray()) {
             if (PAIRS.containsValue(ch)) {
                 stack.push(ch);
             } else if (PAIRS.containsKey(ch)) {
-                if (stack.isEmpty() || stack.pop() != PAIRS.get(ch)) return false;
+                if (stack.isEmpty() || stack.pop() != PAIRS.get(ch)) {
+                    return false;
+                }
             }
         }
         return stack.isEmpty();