Issue #3224032 by shobhit_juyal: Notice: Undefined index: instance_url

src/SalesforceAuthProviderPluginBase.php

@@ -280,7 +280,7 @@ abstract class SalesforceAuthProviderPluginBase extends Salesforce implements Sa
    * {@inheritdoc}
    */
   public function getInstanceUrl() {
-    return $this->getAccessToken()->getExtraParams()['instance_url'];
+    return $this->getAccessToken()->getExtraParams()['instance_url'] ?? '';
   }
 
   /**