The ‘Send Email’ action can be set up to send emails to the employees who have a valid email address.There are chances for the cases in which the employee record may not have the email. In such a scenario, the send email action fails to perform and thus it will affect the working of the entire workflow.
This issue can be resolved by adding condition in the send email action as shown below.

Using this condition, the send email action will trigger only if there is email in the corresponding employee record. And the workflow will skip this action and processes other steps if the email field in the employee record is empty.