+ * In PHP versions before 7.1, decoding a JSON string containing an empty key
+ * without passing $assoc as true results in a return object with a property
+ * named "_empty_" (because true empty properties were not supported pre-PHP-7.1).
+ * Instead, consider passing $assoc as true to return an associative array.
+ *
+ * But be aware that in all supported PHP versions, decoding an empty JSON object
+ * with $assoc = true returns an array, not an object, breaking round-trip consistency.
+ *
+ * See https://phabricator.wikimedia.org/T206411 for more details on these quirks.
+ *