Fix notice in DatasetManager

composer.json

@@ -15,6 +15,11 @@
         }
     ],
     "bin": [ "bin/dataset-info" ],
+    "require": {
+        "php": "^7.4|^8.0",
+        "ext-simplexml": "*",
+        "ext-json": "*"
+    },
     "require-dev": {
         "phpunit/phpunit": "^9.5",
         "phpstan/phpstan": "^1.8"

src/DatasetManager.php

@@ -84,7 +84,7 @@ class DatasetManager
         if (file_exists($fn)) {
             $versions = include $fn;
             foreach ($versions['versions'] as $name=>$version) {
-                self::$packageVersions[$name] = $version['version'];
+                self::$packageVersions[$name] = array_key_exists('version',$version) ? $version['version'] : null;
             }
         }