select box validation struts2

Question

i have form conating a select tag foe example.... "s:select headerKey="" headerValue="Select Gender" key="gender" list="#{'M':'Male','F':'Female'}" /"

and in validation.xml i have the following code....

"field name="gender" field-validator type="requiredstring" message hello /message /field-validator /field"

the slect box is getting validated on client......but the problem is when i submit the form one more validation of same form takes place on server which throws select box is empty.... can anone please help me with this issue.....