OPTUS_ContactUsForm: User can't submit the form if user selects "How Would You Like To Be Contacted" as either and blank email address

User can't submit the form if user selects "How Would You Like To Be Contacted" as either and blank email address.

1.Access the website -http://www.cust2-qa-domain.com:9995/

2.Enter contact name ,phone number and keep email address Blank

3.Select the option "How Would You Like To Be Contacted" as Either and click SUBMIT button.

Actual result :

It shows validation message for email address - "Email address too short to be valid. "

See attached snapshot.

Expected result:

User should submit the form successfully.