--- /tmp/JKHP-36.java	2026-09-01 05:49:06.918084379 +0000
+++ /tmp/JKHP-38.java	2026-09-01 05:49:07.316071776 +0000
@@ -19,6 +19,9 @@
     public static final String SHA_256 = "SHA-256";
 
     public JoinKeyHashPair(String joinKey) {
+        if (joinKey == null || joinKey.isBlank()) {
+            throw new IllegalArgumentException("Join key must not be null or blank");
+        }
         KeyUtils.validateHexEncoding((String)joinKey);
         this.joinKey = joinKey;
     }