HexUtils: fix empty string handling (#1907)

Fixes #1903

Signed-off-by: Markus Rathgeb <maggu2810@gmail.com>

bundles/org.openhab.core/src/main/java/org/openhab/core/util/HexUtils.java

@@ -92,6 +92,10 @@ public class HexUtils {
      * @return the corresponding byte array
      */
     public static byte[] hexToBytes(String hexString, String delimiter) {
+        if (hexString.isEmpty()) {
+            return new byte[0];
+        }
+
         // first convert to upper case to ease the rest
         String ucHexString = hexString.toUpperCase();
 

bundles/org.openhab.core/src/test/java/org/openhab/core/util/HexUtilsTest.java

@@ -12,7 +12,7 @@
  */
 package org.openhab.core.util;
 
-import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.*;
 
 import org.junit.jupiter.api.Test;
 
@@ -62,4 +62,12 @@ public class HexUtilsTest {
         byte[] result = HexUtils.hexToBytes("41-:-42-:-43-:-44", "-:-");
         assertEquals("ABCD", new String(result));
     }
+
+    @Test
+    public void testEmptyByteArray() {
+        final byte[] input = new byte[0];
+        final String str = HexUtils.bytesToHex(input);
+        final byte[] output = HexUtils.hexToBytes(str);
+        assertArrayEquals(input, output);
+    }
 }