fix(A1Z26): return empty string instead of empty array for empty input

src/core/operations/A1Z26CipherDecode.mjs

@@ -76,7 +76,7 @@ class A1Z26CipherDecode extends Operation {
         const delim = Utils.charRep(args[0] || "Space");
 
         if (input.length === 0) {
-            return [];
+            return "";
         }
 
         const bites = input.split(delim);

tests/operations/index.mjs

@@ -14,6 +14,7 @@
 import { setLongTestFailure, logTestReport } from "../lib/utils.mjs";
 
 import TestRegister from "../lib/TestRegister.mjs";
+import "./tests/A1Z26CipherDecode.mjs";
 import "./tests/AESKeyWrap.mjs";
 import "./tests/AlternatingCaps.mjs";
 import "./tests/AvroToJSON.mjs";

tests/operations/tests/A1Z26CipherDecode.mjs

@@ -0,0 +1,33 @@
+/**
+ * A1Z26 Cipher Decode tests
+ *
+ * @author brick-pixel
+ * @copyright Crown Copyright 2026
+ * @license Apache-2.0
+ */
+import TestRegister from "../../lib/TestRegister.mjs";
+
+TestRegister.addTests([
+    {
+        "name": "A1Z26 Cipher Decode: basic decode",
+        "input": "8 5 12 12 15",
+        "expectedOutput": "hello",
+        "recipeConfig": [
+            {
+                "op": "A1Z26 Cipher Decode",
+                "args": ["Space"]
+            }
+        ]
+    },
+    {
+        "name": "A1Z26 Cipher Decode: empty input returns empty string",
+        "input": "",
+        "expectedOutput": "",
+        "recipeConfig": [
+            {
+                "op": "A1Z26 Cipher Decode",
+                "args": ["Space"]
+            }
+        ]
+    }
+]);