Issue #3068584 by Matroskeen, jhchnc, gapple, azussman: item_selector failing...

Issue #3068584 by Matroskeen, jhchnc, gapple, azussman: item_selector failing to grab a inner level JSON array

src/Plugin/migrate_plus/data_parser/Json.php

@@ -51,7 +51,7 @@ class Json extends DataParserPluginBase implements ContainerFactoryPluginInterfa
     // Otherwise, we're using xpath-like selectors.
     $selectors = explode('/', trim((string) $this->itemSelector, '/'));
     foreach ($selectors as $selector) {
-      if ((!empty($selector) || $selector === '0') && array_key_exists($selector, $source_data)) {
+      if (is_array($source_data) && array_key_exists($selector, $source_data)) {
         $source_data = $source_data[$selector];
       }
     }