Check for good WC_Orders before using instance methods.

plugins/woocommerce-admin/includes/class-wc-admin-order-refund.php

@@ -45,13 +45,13 @@ class WC_Admin_Order_Refund extends WC_Order_Refund {
 	/**
 	 * Get the customer ID of the parent order used for reports in the customer lookup table.
 	 *
-	 * @return int
+	 * @return int|bool Customer ID of parent order, or false if parent order not found.
 	 */
 	public function get_report_customer_id() {
 		$parent_order = wc_get_order( $this->get_parent_id() );
 
 		if ( ! $parent_order ) {
-			return null;
+			return false;
 		}
 
 		return WC_Admin_Reports_Customers_Data_Store::get_or_create_customer_from_order( $parent_order );

plugins/woocommerce-admin/includes/data-stores/class-wc-admin-reports-customers-data-store.php

@@ -438,11 +438,12 @@ class WC_Admin_Reports_Customers_Data_Store extends WC_Admin_Reports_Data_Store
 	 * @return int|bool
 	 */
 	public static function get_existing_customer_id_from_order( $order ) {
-		if ( ! $order ) {
+		global $wpdb;
+
+		if ( ! is_a( $order, 'WC_Order' ) ) {
 			return false;
 		}
 
-		global $wpdb;
 		$user_id = $order->get_customer_id();
 
 		if ( 0 === $user_id ) {
@@ -481,6 +482,11 @@ class WC_Admin_Reports_Customers_Data_Store extends WC_Admin_Reports_Data_Store
 		}
 
 		global $wpdb;
+
+		if ( ! is_a( $order, 'WC_Order' ) ) {
+			return false;
+		}
+
 		$returning_customer_id = self::get_existing_customer_id_from_order( $order );
 
 		if ( $returning_customer_id ) {

plugins/woocommerce-admin/includes/data-stores/class-wc-admin-reports-orders-stats-data-store.php

@@ -436,9 +436,11 @@ class WC_Admin_Reports_Orders_Stats_Data_Store extends WC_Admin_Reports_Data_Sto
 		);
 
 		if ( 'shop_order_refund' === $order->get_type() ) {
-			$parent_order      = wc_get_order( $order->get_parent_id() );
-			$data['parent_id'] = $parent_order->get_id();
-			$format[]          = '%d';
+			$parent_order = wc_get_order( $order->get_parent_id() );
+			if ( $parent_order ) {
+				$data['parent_id'] = $parent_order->get_id();
+				$format[]          = '%d';
+			}
 		} else {
 			$data['returning_customer'] = self::is_returning_customer( $order );
 		}

plugins/woocommerce-admin/tests/api/orders.php

@@ -56,4 +56,30 @@ class WC_Tests_API_Orders extends WC_REST_Unit_Test_Case {
 		$this->assertEquals( 200, $response->get_status() );
 		$this->assertEquals( $order->get_id(), $orders[0]['id'] );
 	}
+
+	/**
+	 * Verify that deleted refund parent orders don't cause
+	 */
+	public function test_refund_parent_order_deleted() {
+		global $wpdb;
+
+		wp_set_current_user( $this->user );
+
+		// Create an order.
+		$order = WC_Helper_Order::create_order( $this->user );
+
+		// Create a refund order.
+		$refund = wc_create_refund(
+			array(
+				'order_id' => $order->get_id(),
+			)
+		);
+
+		// Forcibly delete the original order.
+		$wpdb->delete( $wpdb->prefix . 'posts', array( 'ID' => $order->get_id() ), array( '%d' ) );
+		clean_post_cache( $order->get_id() );
+
+		// Trigger an order sync on the refund which should handle the missing parent order.
+		$this->assertTrue( WC_Admin_Reports_Orders_Stats_Data_Store::sync_order( $refund->get_id() ) );
+	}
 }

plugins/woocommerce-admin/tests/api/reports-customers.php

@@ -418,4 +418,12 @@ class WC_Tests_API_Reports_Customers extends WC_REST_Unit_Test_Case {
 		$this->assertCount( 1, $reports );
 		$this->assertEquals( 'Daenerys Targaryen', $reports[0]['name'] );
 	}
+
+	/**
+	 * Test that bad order params don't cause PHP errors when retrieving customers.
+	 */
+	public function test_customer_retrieval_from_order_bad_order() {
+		$this->assertFalse( WC_Admin_Reports_Customers_Data_Store::get_existing_customer_id_from_order( false ) );
+		$this->assertFalse( WC_Admin_Reports_Customers_Data_Store::get_or_create_customer_from_order( false ) );
+	}
 }