Define contributionRecur property on IPN class

CRM/Core/Payment/MJWIPNTrait.php

@@ -34,6 +34,12 @@ trait CRM_Core_Payment_MJWIPNTrait {
    */
   protected $contribution_recur_id = NULL;
 
+  /**
+   * The recurring contribution detail (as retrieved by API4)
+   * @var array
+   */
+  protected $contributionRecur = [];
+
   /**
    *  The IPN event type
    * @var string