diff --git a/src/main/java/com/thealgorithms/strings/Upper.java b/src/main/java/com/thealgorithms/strings/Upper.java index 102d3a190..8f306a20e 100644 --- a/src/main/java/com/thealgorithms/strings/Upper.java +++ b/src/main/java/com/thealgorithms/strings/Upper.java @@ -19,6 +19,9 @@ public class Upper { * @return the {@code String}, converted to uppercase. */ public static String toUpperCase(String s) { + if (s == null || "".equals(s)) { + return s; + } char[] values = s.toCharArray(); for (int i = 0; i < values.length; ++i) { if (Character.isLetter(values[i]) && Character.isLowerCase(values[i])) {