test: CountCharTest (#5423)

test: CountCharTest

Co-authored-by: alxkm <alx@alx.com>

src/main/java/com/thealgorithms/others/CountChar.java

@@ -5,13 +5,16 @@ public final class CountChar {
     }
 
     /**
-     * Count non space character in string
+     * Counts the number of non-whitespace characters in the given string.
      *
-     * @param str String to count the characters
-     * @return number of character in the specified string
+     * @param str the input string to count the characters in
+     * @return the number of non-whitespace characters in the specified string;
+     *         returns 0 if the input string is null
      */
-
     public static int countCharacters(String str) {
+        if (str == null) {
+            return 0;
+        }
         return str.replaceAll("\\s", "").length();
     }
 }